Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 289	$ 282	$ 278	$ 271	$ 1,120	$ 1,053	$ 1,015
Expenses:
Operating and administrative					1,920	1,776	1,697
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues					985	1,243	1,746
Depreciation on operating leases					(68)	106	(75)
Interest expense:
Credit support fees, interest and other expenses					103	96	99
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums					152	156	168
Investment and other income, net:
Interest and other income					62	35	3
Expenses:
Operating and administrative					$ 94	$ 107	$ 82