Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues		$ 226	$ 220	$ 676	$ 657
Expenses:
Operating and administrative expenses		347	323	1,019	973
TMCC-affiliated companies [Member]
Total financing revenues:
Manufacturers’ subvention and other revenues		508	415	1,452	1,165
Interest expense:
Credit support fees, interest and other expenses		24	23	73	71
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues		46	46	135	135
Investment and other income, net:
Interest and other income		4	3	8	10
Expenses:
Operating and administrative expenses		24	19	71	61
Insurance losses and loss adjustment expenses	[1]	$ 0	$ 1	$ (3)	$ (3)

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