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) - Fair Value, Measurements, Nonrecurring ¥ in Millions	Sep. 30, 2024 JPY (¥)	Mar. 31, 2024 JPY (¥)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	¥ 2,908	¥ 5,535
Investment in operating leases and property under facility operations	169	1,205
Certain equity method investments	1,285	461
Assets measured at fair value on a nonrecurring basis	17,132	27,391
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	2,908	5,274
Investment in operating leases and property under facility operations	169	1,205
Certain equity method investments	1,285	461
Assets measured at fair value on a nonrecurring basis	4,362	6,940
Level 3 | Direct capitalization | Capitalization rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	1,064	892
Level 3 | Discounted cash flows | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in operating leases and property under facility operations		337
Level 3 | Appraisals
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate collateral-dependent loans (net of allowance for credit losses)	1,844	4,382
Investment in operating leases and property under facility operations	169	868
Certain equity method investments	¥ 1,285
Level 3 | Market Multiples | EV/EBITDA multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Certain equity method investments		¥ 461
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)	0.046	0.046
Level 3 | Minimum | 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		0
Level 3 | Minimum | Market Multiples | EV/EBITDA multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Certain equity method investments		3
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)	0.065	0.063
Level 3 | Maximum | 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		0.13
Level 3 | Maximum | Market Multiples | EV/EBITDA multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Certain equity method investments		6
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)	0.052	0.053
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, Investment in operating leases, property under facility operations		0.036
Level 3 | Weighted Average | Market Multiples | EV/EBITDA multiple
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant unobservable inputs, Certain equity method investments		4.5