Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Total financing revenues:
Manufacturers’ subvention and other revenues	$ 415	$ 349	$ 1,165	$ 1,019
Interest expense:
Credit support fees incurred	23	22	70	68
Interest and other expenses	0	0	1	1
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues	220	202	657	594
Expenses:
Operating and administrative	323	325	973	921
TMCC-affiliated companies [Member]
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues	46	36	135	105
Investment and other income, net:
Interest and other income	3	1	10	6
Expenses:
Operating and administrative	19	18	61	52
Insurance losses and loss adjustment expenses	$ 1	$ 0	$ (3)	$ 1