v3.26.1
Goodwill and Intangible Assets - Schedule of Changes in Goodwill and Intangible Assets (Details) - JPY (¥)
¥ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Goodwill, beginning balance ¥ 15,157  
Intangible assets, beginning balance (65,672)  
Goodwill, ending balance 15,157 ¥ 15,157
Intangible assets, ending balance (66,466) (65,672)
Acquisition Cost    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Goodwill, beginning balance 15,157 9,919
Intangible assets, beginning balance (132,450) (118,307)
Goodwill, acquisitions   5,238
Intangible assets, acquisitions 8,191 9,973
Intangible assets, internal development 9,373 7,566
Intangible assets, disposals 7,357 3,126
Intangible assets, other (113) (270)
Goodwill, ending balance 15,157 15,157
Intangible assets, ending balance (142,544) (132,450)
Acquisition Cost | Software    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (123,822) (110,198)
Intangible assets, acquisitions 4,382 4,794
Intangible assets, internal development   193
Intangible assets, transfers from software in progress 10,045 11,767
Intangible assets, disposals 7,282 3,047
Intangible assets, other (75) (83)
Intangible assets, ending balance (130,892) (123,822)
Acquisition Cost | Software in progress    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (3,004) (3,582)
Intangible assets, acquisitions 3,809 4,082
Intangible assets, internal development 9,373 7,373
Intangible assets, transfers from software in progress (10,045) (11,767)
Intangible assets, disposals 75 79
Intangible assets, other (38) (187)
Intangible assets, ending balance (6,028) (3,004)
Acquisition Cost | Customer Relationship    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (5,624) (4,527)
Intangible assets, acquisitions   1,097
Intangible assets, ending balance (5,624) (5,624)
Accumulated Amortisation and Impairment Losses    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance 66,778 56,617
Intangible assets, amortization 15,912 13,171
Intangible assets, disposals (6,612) (3,024)
Intangible assets, other   14
Intangible assets, ending balance 76,078 66,778
Accumulated Amortisation and Impairment Losses | Software    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance 63,356 53,633
Intangible assets, amortization 15,430 12,733
Intangible assets, disposals (6,612) (3,024)
Intangible assets, other   14
Intangible assets, ending balance 72,174 63,356
Accumulated Amortisation and Impairment Losses | Software in progress    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance 224 224
Intangible assets, ending balance 224 224
Accumulated Amortisation and Impairment Losses | Customer Relationship    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance 3,198 2,760
Intangible assets, amortization 482 438
Intangible assets, ending balance 3,680 3,198
Book Value    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Goodwill, beginning balance 15,157  
Intangible assets, beginning balance (65,672)  
Goodwill, ending balance 15,157 15,157
Intangible assets, ending balance (66,466) (65,672)
Book Value | Software    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (60,466)  
Intangible assets, ending balance (58,718) (60,466)
Book Value | Software in progress    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (2,780)  
Intangible assets, ending balance (5,804) (2,780)
Book Value | Customer Relationship    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Intangible assets, beginning balance (2,426)  
Intangible assets, ending balance ¥ (1,944) ¥ (2,426)