v3.26.1
Financial instruments - Summary of Fair Values by Fair Value Hierarchy Level of Certain Financial Instruments that are Measured at Amortized Cost (Detail) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Debt securities    
Total assets ¥ 15,683,490 ¥ 35,293,173
Liabilities    
Long-term debt including the current portion 990,803 1,754,817
Total liabilities 7,169,901 26,783,022
Financial liabilities at amortised cost, category [member] | At fair value [member]    
Liabilities    
Long-term debt including the current portion 964,534 1,722,896
Investment contract liabilities   60,558
Total liabilities 964,534 1,783,454
Financial liabilities at amortised cost, category [member] | Carrying amount [member]    
Liabilities    
Long-term debt including the current portion 990,803 1,754,817
Investment contract liabilities   62,772
Total liabilities 990,803 1,817,589
Financial liabilities at amortised cost, category [member] | Level 2 [Member] | At fair value [member]    
Liabilities    
Long-term debt including the current portion 962,660 1,621,264
Investment contract liabilities   60,558
Total liabilities 962,660 1,681,822
Financial liabilities at amortised cost, category [member] | Level 3 [Member] | At fair value [member]    
Liabilities    
Long-term debt including the current portion 1,874 101,632
Total liabilities ¥ 1,874 101,632
Financial assets at amortised cost, category [member] | At fair value [member]    
Assets    
Housing Loans in the Banking Business   3,709,148
Debt securities    
Total assets   4,229,370
Financial assets at amortised cost, category [member] | Carrying amount [member]    
Assets    
Housing Loans in the Banking Business   3,763,261
Debt securities    
Total assets   4,284,315
Financial assets at amortised cost, category [member] | Level 2 [Member] | At fair value [member]    
Debt securities    
Total assets   66,726
Financial assets at amortised cost, category [member] | Level 3 [Member] | At fair value [member]    
Assets    
Housing Loans in the Banking Business   3,709,148
Debt securities    
Total assets   4,162,644
Financial assets at amortised cost, category [member] | Japanese local government bonds [Member] | At fair value [member]    
Debt securities    
Debt instruments held   11,696
Financial assets at amortised cost, category [member] | Japanese local government bonds [Member] | Carrying amount [member]    
Debt securities    
Debt instruments held   11,626
Financial assets at amortised cost, category [member] | Japanese local government bonds [Member] | Level 2 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   11,696
Financial assets at amortised cost, category [member] | Japanese Corporate Bonds [Member] | At fair value [member]    
Debt securities    
Debt instruments held   24,273
Financial assets at amortised cost, category [member] | Japanese Corporate Bonds [Member] | Carrying amount [member]    
Debt securities    
Debt instruments held   24,916
Financial assets at amortised cost, category [member] | Japanese Corporate Bonds [Member] | Level 2 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   24,273
Financial assets at amortised cost, category [member] | Foreign Corporate Bonds [Member] | At fair value [member]    
Debt securities    
Debt instruments held   937
Financial assets at amortised cost, category [member] | Foreign Corporate Bonds [Member] | Carrying amount [member]    
Debt securities    
Debt instruments held   935
Financial assets at amortised cost, category [member] | Foreign Corporate Bonds [Member] | Level 2 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   937
Financial assets at amortised cost, category [member] | Securitized Products [Member] | At fair value [member]    
Debt securities    
Debt instruments held   439,132
Financial assets at amortised cost, category [member] | Securitized Products [Member] | Carrying amount [member]    
Debt securities    
Debt instruments held   439,281
Financial assets at amortised cost, category [member] | Securitized Products [Member] | Level 3 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   439,132
Financial assets at amortised cost, category [member] | Other Debt Securities [Member] | At fair value [member]    
Debt securities    
Debt instruments held   44,184
Financial assets at amortised cost, category [member] | Other Debt Securities [Member] | Carrying amount [member]    
Debt securities    
Debt instruments held   44,296
Financial assets at amortised cost, category [member] | Other Debt Securities [Member] | Level 2 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   29,820
Financial assets at amortised cost, category [member] | Other Debt Securities [Member] | Level 3 [Member] | At fair value [member]    
Debt securities    
Debt instruments held   ¥ 14,364