v3.25.2
Property and equipment (Details) - JPY (¥)
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period ¥ 1,973,000,000 ¥ 644,000,000
Property, plant and equipment including right-of-use assets at end of period 1,909,000,000 1,973,000,000
Retirements, right-of-use assets 339,000,000 35,000,000
Property, plant and equipment, pledged as collateral 0  
Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 3,000,000 85,000,000
Property, plant and equipment including right-of-use assets at end of period 338,000,000 3,000,000
Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 24,000,000 54,000,000
Property, plant and equipment including right-of-use assets at end of period 32,000,000 24,000,000
Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 299,000,000 0
Property, plant and equipment including right-of-use assets at end of period 0 299,000,000
Gross carrying amount    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 3,672,000,000 2,179,000,000
Additions 549,000,000 2,065,000,000
Decrease due to lease term changes   (82,000,000)
Sales and disposals (1,500,000,000) (490,000,000)
Additions (transferred from Construction in progress) 0  
Additions (business combination) 2,000,000  
Property, plant and equipment including right-of-use assets at end of period 2,725,000,000 3,672,000,000
Gross carrying amount | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 253,000,000 455,000,000
Property, plant and equipment including right-of-use assets at end of period 542,000,000 253,000,000
Gross carrying amount | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 149,000,000 189,000,000
Property, plant and equipment including right-of-use assets at end of period 121,000,000 149,000,000
Gross carrying amount | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 299,000,000 0
Property, plant and equipment including right-of-use assets at end of period 0 299,000,000
Accumulated depreciation, amortisation and impairment    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (1,700,000,000) (1,535,000,000)
Sales and disposals 1,496,000,000 360,000,000
Property, plant and equipment including right-of-use assets at end of period (815,000,000) (1,700,000,000)
Accumulated depreciation, amortisation and impairment | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (100,000,000) (25,000,000)
Accumulated depreciation, amortisation and impairment | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (511,000,000) (500,000,000)
Accumulated depreciation, amortisation and impairment | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (250,000,000) (370,000,000)
Property, plant and equipment including right-of-use assets at end of period (204,000,000) (250,000,000)
Accumulated depreciation, amortisation and impairment | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (125,000,000) (135,000,000)
Property, plant and equipment including right-of-use assets at end of period (89,000,000) (125,000,000)
Accumulated depreciation, amortisation and impairment | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 0 0
Property, plant and equipment including right-of-use assets at end of period 0 0
Property, plant and equipment | Gross carrying amount | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 4,000,000 0
Decrease due to lease term changes   0
Sales and disposals (123,000,000) (202,000,000)
Additions (transferred from Construction in progress) 406,000,000  
Additions (business combination) 2,000,000  
Property, plant and equipment | Gross carrying amount | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 7,000,000 4,000,000
Decrease due to lease term changes   0
Sales and disposals (48,000,000) (44,000,000)
Additions (transferred from Construction in progress) 13,000,000  
Additions (business combination) 0  
Property, plant and equipment | Gross carrying amount | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 120,000,000 303,000,000
Decrease due to lease term changes   0
Sales and disposals 0 (4,000,000)
Additions (transferred from Construction in progress) (419,000,000)  
Additions (business combination) 0  
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 123,000,000 194,000,000
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (77,000,000) (74,000,000)
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 44,000,000 30,000,000
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (8,000,000) (20,000,000)
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Right-of-use assets    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 1,647,000,000 505,000,000
Property, plant and equipment including right-of-use assets at end of period 1,539,000,000 1,647,000,000
Right-of-use assets | Gross carrying amount    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 2,972,000,000 1,535,000,000
Additions 418,000,000 1,758,000,000
Decrease due to lease term changes   (82,000,000)
Sales and disposals (1,329,000,000) (240,000,000)
Additions (transferred from Construction in progress) 0  
Additions (business combination) 0  
Property, plant and equipment including right-of-use assets at end of period 2,062,000,000 2,972,000,000
Right-of-use assets | Accumulated depreciation, amortisation and impairment    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (1,325,000,000) (1,030,000,000)
Sales and disposals 1,329,000,000 136,000,000
Property, plant and equipment including right-of-use assets at end of period (522,000,000) (1,325,000,000)
Right-of-use assets | Accumulated depreciation, amortisation and impairment | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (100,000,000) (25,000,000)
Right-of-use assets | Accumulated depreciation, amortisation and impairment | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment ¥ (426,000,000) ¥ (406,000,000)