Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 303	$ 282	$ 898	$ 831
Expenses:
Operating and administrative	451	517	1,344	1,414
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	252	237	716	760
Depreciation on operating leases	3	5	24	(82)
Interest expense:
Credit support fees, interest and other expenses	29	29	86	77
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	48	39	131	116
Investment and other income, net:
Interest and other (loss) income	(3)	26	45	45
Expenses:
Operating and administrative	$ 26	$ 26	$ 78	$ 72