Shareholdings
| Concept | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Shareholdings | ||||||||||||||||||||||||||||||||||
| Reporting company | ||||||||||||||||||||||||||||||||||
| Details of specified investment shares held for purposes other than pure investment | ||||||||||||||||||||||||||||||||||
| Issue | 
                                                SOMPOホールディングス㈱
                                                
                                             | 
                                                TREホールディングス㈱
                                                
                                             | 
                                                ㈱横河ブリッジホールディングス
                                                
                                             | 
                                                ㈱三井住友フィナンシャルグループ
                                                
                                             | 
                                                ㈱協和日成
                                                
                                             | 
                                                ㈱三菱UFJフィナンシャルグループ
                                                
                                             | 
                                                ㈱みずほフィナンシャルグループ
                                                
                                             | 
                                                応用地質㈱
                                                
                                             | 
                                                東京電力ホールディングス㈱
                                                
                                             | 
                                                野村ホールディングス㈱
                                                
                                             | 
                                                第一生命ホールディングス㈱
                                                
                                             | 
                                                DNホールディングス㈱
                                                
                                             | 
                                                三井住友トラスト・ホールディングス㈱(注)
                                                
                                             | 
                                                ㈱りそなホールディングス
                                                
                                             | 
                                                ㈱オオバ
                                                
                                             | 
                                                ㈱建設技術研究所
                                                
                                             | 
                                                ㈱オリエンタルコンサルタンツホールディングス
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Number of shares | 
                                                7,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                24,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                30,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                8,850
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                48,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                19,870
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                2,072
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                9,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                30,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                5,515
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                1,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                24,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                60,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                17,125
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                100,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                96,136
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                70,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                17,125
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                2,072
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                96,136
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                7,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                24,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                30,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                9,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                8,850
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                30,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                48,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                19,870
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                5,515
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                24,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                1,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                30,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                100,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                70,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
| Carrying amount | 
                                                51,720,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                27,280,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                76,110,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                60,888,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                60,336,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                24,072,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,998,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                20,109,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                22,155,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,516,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,188,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                33,936,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                162,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,270,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                91,800,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                505,675,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                190,050,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,384,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                308,596,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                43,950,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                35,240,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                56,310,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                22,363,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                46,869,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                14,280,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                67,920,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                17,664,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,694,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                30,240,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,191,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                137,640,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                65,400,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                188,370,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Whether issuer of aforementioned shares holds reporting company's shares | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                無
                                                
                                             | 
                                                有
                                                
                                             | 
                                                無
                                                
                                             | 
                                                無
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | 
                                                有
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |