Income Taxes - Deferred Tax Liabilities and Assets (Details) - USD ($) $ in Millions		Mar. 31, 2025	Mar. 31, 2024
Liabilities:
Lease transactions		$ 3,181	$ 3,493
Voluntary protection dealer commissions		485	439
State taxes, net of federal tax benefit		237	271
Other		101	73
Deferred tax liabilities		4,004	4,276
Assets:
Provision for credit and residual value losses		503	517
Deferred costs and fees		235	210
Mark-to-market of investments in marketable securities and derivatives		171	186
Lease obligations		38	19
Accrued expenses		26	40
Net operating loss and tax credit carryforwards		15	14
Other		43	19
Deferred tax assets		1,031	1,005
Valuation allowance		0	(1)
Net deferred tax assets		1,031	1,004
Net deferred income tax liability	[1]	$ 2,973	$ 3,272

[1] Balance includes deferred tax assets of $15 million and $18 million at March 31, 2025 and 2024, respectively, attributable to unrealized losses included in accumulated other comprehensive loss. The change in this balance is not included in the total deferred tax expense.