Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 300	$ 278	$ 595	$ 549
Expenses:
Operating and administrative	453	449	893	897
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	239	253	464	523
Depreciation on operating leases	4	(118)	21	(87)
Interest expense:
Credit support fees, interest and other expenses	28	24	57	48
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	42	39	83	77
Investment and other income, net:
Interest and other income	35	11	48	19
Expenses:
Operating and administrative	$ 26	$ 22	$ 52	$ 46