Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013
Net financing revenues:
Manufacturer's subvention support and other revenues	$ 250	$ 236	$ 482	$ 462
Credit support fees incurred	(20)	(27)	(40)	(35)
Foreign exchange gain (loss) on loans payable to affiliates	0	0	0	(39)
Interest expense on loans payable to affiliates	(1)	(1)	(1)	(4)
Insurance earned premiums and contract revenues:
Affiliate insurance premiums and contract revenues	33	43	66	92
Investments and other income, net:
Interest earned on notes receivable from affiliates	2	2	3	3
Expenses:
Shared services charges and other expenses	16	16	30	32
Employee benefits expense	9	8	18	15
Investment in marketable securities
Investments in affiliates commercial paper	5		5		2
Finance receivables, net
Accounts receivable from affiliates	67		67		22
Direct finance receivables from affiliates	6		6		6
Notes receivable under home loan programs	17		17		18
Deferred retail subvention income from affiliates	(782)		(782)		(699)
Investments in operating leases, net
Leases to affiliates	7		7		7
Deferred lease subvention income from affiliates	(728)		(728)		(604)
Other assets
Notes receivable from alliliates	1,288		1,288		931
Other receivables from affiliates	2		2		1
Subvention support receivable from affiliates	158		158		88
Debt:
Loans payable to affiliate	0		0		0
Other liabilities
Unearned affiliates insurance premiums and contract revenues	241		241		235
Accounts payable to affiliates	148		148		192
Notes payable to affiliate	53		53		48
Shareholder's Equity:
Dividends paid	665				1,487
Stock based compensation	$ 2				$ 2