Related Party Transactions - Related Party Transactions Included in Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Cash and cash equivalents
Cash and cash equivalents	$ 3,540	$ 4,198	$ 2,701	$ 2,407
Finance receivables, net
Accounts receivable	191	138
Deferred retail subvention income	(1,279)	(967)
Investments in operating leases, net
Investments in operating leases, net	38,697	38,152
Deferred lease subvention income	(1,682)	(1,174)
Other assets
Notes receivable from affiliates	68	823
Other receivables, net	310	202
Other liabilities
Unearned insurance premiums and contract revenues	2,271	2,154
Other payables, net	74	74
Notes payable	18	13
Commercial paper [Member]
Cash and cash equivalents
Cash and cash equivalents	255	0
TMCC-affiliated companies [Member]
Investments in marketable securities
Commercial paper	52	0
Investments in operating leases, net
Investments in operating leases, net	6	4
Other liabilities
Unearned insurance premiums and contract revenues	$ 328	$ 332