Fair Value Measurements (Information about Valuation Techniques and Significant Unobservable Inputs Used in Valuation of Level Three Assets Measured at Fair Value on Nonrecurring Basis) (Detail) ¥ in Millions	Sep. 30, 2025 JPY (¥)	Mar. 31, 2025 JPY (¥)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	¥ 85,724	¥ 97,694
Investment in Operating Leases	2,086,405	1,967,178
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	168
Real estate collateral-dependent loans (net of allowance for credit losses)	3,490	5,881
Investment in Operating Leases	234
Certain equity method investments	1,109	20,619
Total	42,466	49,798
Fair Value, Measurements, Nonrecurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	121
Real estate collateral-dependent loans (net of allowance for credit losses)	3,490	5,881
Investment in Operating Leases	234
Certain equity method investments	1,109	20,619
Total	4,954	34,605
Fair Value, Measurements, Nonrecurring \| Level 3 \| Direct capitalization
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	1,142	1,064
Fair Value, Measurements, Nonrecurring \| Level 3 \| Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	121
Investment in operating leases, property under facility operations and office facilities		¥ 3,314
Fair Value, Measurements, Nonrecurring \| Level 3 \| Discounted cash flows \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Investment in operating leases, property under facility operations and office facilities		0.061
Fair Value, Measurements, Nonrecurring \| Level 3 \| Appraisals/Broker quotes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	2,348	¥ 4,817
Investment in operating leases, property under facility operations and office facilities		4,791
Investment in Operating Leases	234
Certain equity method investments	¥ 1,109	¥ 20,619
Fair Value, Measurements, Nonrecurring \| Level 3 \| Minimum \| Direct capitalization \| Capitalization rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Real estate collateral-dependent loans (net of allowance for credit losses)	0.047	0.044
Fair Value, Measurements, Nonrecurring \| Level 3 \| Minimum \| Discounted cash flows \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Loans held for sale	0.05
Fair Value, Measurements, Nonrecurring \| Level 3 \| Maximum \| Direct capitalization \| Capitalization rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Real estate collateral-dependent loans (net of allowance for credit losses)	0.055	0.052
Fair Value, Measurements, Nonrecurring \| Level 3 \| Maximum \| Discounted cash flows \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Loans held for sale	0.08
Fair Value, Measurements, Nonrecurring \| Level 3 \| Weighted Average \| Direct capitalization \| Capitalization rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Real estate collateral-dependent loans (net of allowance for credit losses)	0.049	0.047
Fair Value, Measurements, Nonrecurring \| Level 3 \| Weighted Average \| Discounted cash flows \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Loans held for sale	0.065
Significant unobservable inputs, Investment in operating leases, property under facility operations and office facilities		0.061

Fair Value Measurements (Information about Valuation Techniques and Significant Unobservable Inputs Used in Valuation of Level Three Assets Measured at Fair Value on Nonrecurring Basis) (Detail)
¥ in Millions