Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 278	$ 263	$ 549	$ 522
Expenses:
Operating and administrative	449	444	897	850
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	253	316	523	655
Depreciation on operating leases	(118)	34	(87)	56
Interest expense:
Credit support fees, interest and other expenses	24	24	48	47
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	39	39	77	79
Investment and other income, net:
Interest and other income	11	3	19	(3)
Expenses:
Operating and administrative	$ 22	$ 16	$ 46	$ 37