Related Party Transactions - Related Party Transactions Included in Consolidated Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Investments in marketable securities
Investments in affiliates' commercial paper	$ 37	$ 0
Finance receivables, net
Accounts receivable from affiliates	83	74
Direct finance lease receivables from affiliates	6	6
Notes receivable under home loan programs	11	15
Deferred retail origination costs paid to affiliates	1	1
Deferred retail subvention income from affiliates	(802)	(768)
Investments in operating leases, net
Leases to affiliates	31,128	24,769
Deferred lease origination costs paid to affiliates	1	0
Deferred lease subvention income from affiliates	(950)	(806)
Other assets:
Notes receivable from affiliates	1,184	1,172
Other receivables from affiliates	6	2
Subvention support receivable from affiliates	126	159
Other liabilities:
Unearned insurance premiums and contract revenues	1,825	1,665
Accounts payable to affiliates	136	216
Notes payable to affiliates	24	22
TMCC-affiliated companies [Member]
Investments in operating leases, net
Leases to affiliates	7	7
Other liabilities:
Unearned insurance premiums and contract revenues	252	244
Shareholder's equity:
Stock-based compensation	$ 2	$ 2