Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Total financing revenues:
Manufacturers’ subvention and other revenues	$ 382	$ 334	$ 750	$ 670
Interest expense:
Credit support fees incurred	24	23	47	46
Interest and other expenses	0	0	1	1
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues	221	199	437	392
Expenses:
Operating and administrative	337	317	650	596
Insurance losses and loss adjustment expenses	102	91	216	180
TMCC-affiliated companies [Member]
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues	45	35	89	69
Investment and other income, net:
Interest and other income	3	3	7	5
Expenses:
Operating and administrative	23	17	42	34
Insurance losses and loss adjustment expenses	$ 1	$ 0	$ (4)	$ 1