Related Party Transactions - Related Party Transactions Included in Consolidated Balance Sheet (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Sep. 30, 2015	Mar. 31, 2015
Investments in marketable securities
Investments in affiliates’ commercial paper	$ 20	$ 37
Finance receivables, net
Accounts receivable from affiliates	102	83
Direct finance lease receivables from affiliates	0	6
Notes receivable under home loan programs	10	11
Deferred retail origination costs paid to affiliates	1	1
Deferred retail subvention income from affiliates	(837)	(802)
Investments in operating leases, net
Leases to affiliates	33,741	31,128
Deferred lease origination costs paid to affiliates	1	1
Deferred lease subvention income from affiliates	(1,058)	(950)
Other assets:
Notes receivable from affiliates	1,007	1,184
Other receivables from affiliates	10	6
Subvention support receivable from affiliates	175	126
Assets held-for-sale	2,127	0
Other liabilities:
Unearned insurance premiums and contract revenues	1,921	1,825
Accounts payable to affiliates	80	136
Notes payable to affiliates	25	24
TMCC-affiliated companies [Member]
Investments in operating leases, net
Leases to affiliates	2	7
Other assets:
Assets held-for-sale	57	0
Other liabilities:
Unearned insurance premiums and contract revenues	260	252
Shareholder’s equity:
Stock-based compensation	$ 2	$ 2