Other Assets and Other Liabilities - Other Assets and Other Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017
Other assets:
Notes receivable from affiliates	$ 68	$ 823
Used vehicles held for sale	366	264
Derivative assets	61	51
Other assets	1,119	906
Total other assets	1,614	2,044
Other liabilities:
Unearned insurance premiums and contract revenues	2,271	2,154
Accounts payable and accrued expenses	1,054	1,057
Deferred income	468	468
Income taxes payable	2	62
Derivative liabilities	6	46
Other liabilities	186	165
Total other liabilities	$ 3,987	$ 3,952