Other Assets and Other Liabilities - Other Assets and Other Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018
Other assets:
Notes receivable from affiliates	$ 56	$ 68
Used vehicles held for sale	420	366
Derivative assets	82	61
Other assets	1,059	1,119
Total other assets	1,617	1,614
Other liabilities:
Unearned insurance premiums and contract revenues	2,522	2,271
Accounts payable and accrued expenses	1,113	1,054
Deferred income	477	468
Income taxes payable	3	2
Derivative liabilities	4	6
Other liabilities	187	186
Total other liabilities	$ 4,306	$ 3,987