Related Party Transactions - Related Party Transactions Included in Consolidated Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net financing revenues:
Manufacturers’ subvention support and other revenues	$ 330	$ 296	$ 647	$ 569
Origination costs paid to affiliates	(1)	0	(1)	0
Credit support fees incurred	(23)	(22)	(45)	(43)
Interest and other expenses paid to affiliates	0	0	(2)	(1)
Insurance earned premiums and contract revenues:
Affiliate insurance premiums and contract revenues	178	160	352	313
Investments and other income, net:
Interest earned on notes receivable from affiliates	2	1	3	2
TMCC-affiliated companies [Member]
Insurance earned premiums and contract revenues:
Affiliate insurance premiums and contract revenues	33	33	65	65
Expenses:
Shared services charges and other expenses	13	16	27	32
Employee benefits expense	$ 8	$ 7	$ 16	$ 13