Quarterly Consolidated Balance Sheet
| Concept | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quarterly consolidated balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash and deposits | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,679,456,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,731,858,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,062,459,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,032,057,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                173,134,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                408,324,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                7,288,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                293,248,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -10,251,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -15,641,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -7,754,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -21,761,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                14,017,562,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,996,988,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                11,737,584,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                7,261,723,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property, plant and equipment | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                11,597,998,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,656,248,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                9,132,194,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                8,157,909,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Property, plant and equipment | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Land | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,974,564,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,274,136,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,944,721,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                3,244,294,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Construction in progress | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                124,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,384,519,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,384,519,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Goodwill | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                991,199,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                991,199,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                421,341,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                421,341,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                21,545,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                15,570,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                21,105,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                15,313,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,132,489,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                114,007,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                603,470,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                152,842,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,848,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                6,718,959,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,062,063,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                5,437,598,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investment securities | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,307,229,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                791,087,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,211,873,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                929,023,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                645,238,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                431,199,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                361,499,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                249,866,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                195,838,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                29,490,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                144,373,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                31,217,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -42,443,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -38,514,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -43,463,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -41,963,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                17,579,417,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                17,489,214,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                13,797,728,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                13,748,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | 
                                                6,657,592,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                121,664,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                13,295,084,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                912,180,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
                                                21,355,615,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                31,596,980,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                26,486,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                20,986,522,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                369,093,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,167,846,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                892,404,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                124,624,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,834,687,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                17,019,562,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                25,535,312,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                17,191,239,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                21,010,073,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                171,676,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Short-term borrowings | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,330,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,140,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,030,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,080,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Income taxes payable | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                760,251,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                459,045,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                533,103,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                325,210,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Asset retirement obligations | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                25,490,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                25,490,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                310,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                12,320,278,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,024,701,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                8,517,050,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                6,321,224,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Long-term borrowings | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,672,517,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,609,796,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,663,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,630,838,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retirement benefit liability | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                146,286,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                152,731,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Asset retirement obligations | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                379,593,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                379,593,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                330,343,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                330,343,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                5,766,827,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,217,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,706,374,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                3,996,373,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                18,087,105,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                15,242,062,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                13,223,425,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                10,317,598,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Shareholders' equity | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share capital | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Capital surplus | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                177,259,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                177,259,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                140,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                140,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                12,182,494,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,123,692,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                10,850,916,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                9,283,103,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Treasury shares | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -264,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -264,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -43,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -43,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                13,096,890,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                11,038,088,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                11,949,403,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                10,381,590,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Valuation and translation adjustments | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Valuation difference on available-for-sale securities | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                435,743,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                206,052,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                390,403,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                310,884,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Remeasurements of defined benefit plans | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -22,759,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -27,919,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Valuation and translation adjustments | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                412,984,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                206,052,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                362,484,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                310,884,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | — | — | 
                                                49,155,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -264,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                177,259,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                206,052,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                95,950,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                435,743,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -22,759,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                11,038,088,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                6,020,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                13,096,890,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                412,984,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -264,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                177,259,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                81,309,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,123,692,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                154,549,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,182,494,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,899,987,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                13,509,874,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                11,244,140,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                206,052,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                52,962,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -27,919,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,381,590,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                95,950,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -43,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,283,103,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                310,884,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                310,884,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                390,403,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                140,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                154,549,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,850,916,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,155,591,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                140,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,920,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -43,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                44,472,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,311,887,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                11,949,403,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                362,484,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,692,475,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                85,494,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                91,475,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,600,158,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                154,549,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,001,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,569,485,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                19,839,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                91,475,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,785,489,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,739,284,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                111,792,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                115,789,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                115,789,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -70,135,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -70,135,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,820,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -26,298,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                95,950,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,870,984,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,647,808,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,737,839,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                56,123,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Liabilities and net assets | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                31,596,980,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                26,486,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                25,535,312,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                21,010,073,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |