Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total financing revenues:
Manufacturers’ subvention and other revenues		$ 472	$ 382	$ 944	$ 750
Interest expense:
Credit support fees, interest and other expenses		24	24	49	48
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues		226	221	450	437
Expenses:
Operating and administrative expenses		348	337	672	650
TMCC-affiliated companies [Member]
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues		44	45	89	89
Investment and other income, net:
Interest and other income		2	3	4	7
Expenses:
Operating and administrative expenses		24	23	47	42
Insurance losses and loss adjustment expenses	[1]	$ (1)	$ 1	$ (3)	$ (4)

[1] Amount includes the transfer of insurance losses and loss adjustment expenses under a reinsurance contract.