Key Financial Data Of Group
| Concept | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | 2023-04-01 to 2024-03-31 | As at 2024-03-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2021-04-01 to 2022-03-31 | As at 2022-03-31 | 2020-04-01 to 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | 2019-04-01 to 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||||||||
| Business results of group | ||||||||||||||
| Ordinary profit (loss) | — | — | — | — | 
                                                1,354,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,074,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,286,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,108,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,653,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets | — | 
                                                11,630,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                10,951,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                10,430,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                9,756,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,114,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | — | 
                                                20,326,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                18,354,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                19,025,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                16,771,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                16,672,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | — | 
                                                972.09
                                                
                                             | — | — | — | — | 
                                                915.39
                                                
                                             | — | — | 
                                                871.80
                                                
                                             | — | 
                                                815.45
                                                
                                             | 
                                                761.82
                                                
                                             | — | 
| Basic earnings (loss) per share | — | — | — | — | 
                                                70.70
                                                
                                             | — | — | 
                                                59.10
                                                
                                             | 
                                                71.13
                                                
                                             | — | 
                                                62.67
                                                
                                             | — | — | 
                                                95.12
                                                
                                             | 
| Diluted earnings per share | — | — | — | — |  | — | — |  |  | — |  | — | — |  | 
| Equity-to-asset ratio | — | 
                                                0.572
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.597
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.548
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.582
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.547
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Rate of return on equity | — | — | — | — | 
                                                0.0749
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.0661
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.0843
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.0795
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.1316
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Price-earnings ratio | — | — | — | — | 
                                                9.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                8.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                7.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                4.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Net cash provided by (used in) operating activities | — | — | — | — | 
                                                -586,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,067,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,383,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,762,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -46,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | — | — | — | 
                                                -52,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -48,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -28,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -42,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                198,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | — | — | — | 
                                                -427,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -358,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -317,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -219,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -268,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | — | 
                                                4,415,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                5,482,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,822,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,785,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,285,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | 
                                                79
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                394
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                73
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                153
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                89
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                387
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                381
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                377
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                372
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |