Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 1,210	$ 1,120	$ 1,053
Expenses:
Operating and administrative	1,827	1,920	1,776
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	975	985	1,243
Depreciation on operating leases	22	(68)	106
Interest expense:
Credit support fees, interest and other expenses	114	103	96
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	181	152	156
Investment and other income, net:
Interest and other income	91	62	35
Expenses:
Operating and administrative	$ 108	$ 94	$ 107