Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net financing revenues:
Depreciation on operating leases	$ (1,499)	$ (1,349)	$ (2,940)	$ (3,034)
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	254	238	503	473
Expenses:
Operating and administrative expenses	385	389	769	734
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	457	502	936	1,001
Depreciation on operating leases	(25)	(26)	(53)	(49)
Interest expense:
Credit support fees, interest and other expenses	27	29	51	67
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	43	43	85	87
Investment and other income, net:
Interest and other income	2	5	5	13
Expenses:
Operating and administrative expenses	$ 22	$ 23	$ 43	$ 43