Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012
Net financing revenues:
Manufacturer's subvention support and other revenues	$ 238	$ 233	$ 700	$ 719
Credit support fees incurred	(18)	(9)	(53)	(25)
Foreign exchange gain (loss) on loans payable to affiliates	0	(3)	(39)	(97)
Interest expense on loans payable to affiliates	(1)	(14)	(5)	(37)
Insurance earned premiums and contract revenues:
Affiliate insurance premiums and contract revenues	36	54	128	163
Investments and other income, net:
Interest earned on notes receivable from affiliates	1	0	4	1
Expenses:
Shared services charges and other expenses	16	16	48	50
Employee benefits expense	7	0	22	20
Investment in marketable securities
Investments in affiliates commercial paper	6		6		0
Finance receivables, net
Accounts receivable from affiliates	24		24		17
Direct finance receivables from affiliates	5		5		4
Notes receivable under home loan programs	19		19		19
Deferred retail subvention income from affiliates	(686)		(686)		(598)
Investments in operating leases, net
Leases to affiliates	5		5		4
Deferred lease subvention income from affiliates	(592)		(592)		(592)
Other assets
Notes receivable from alliliates	1,681		1,681		1,052
Other receivables from affiliates	1		1		8
Subvention support receivable from affiliates	94		94		65
Debt:
Loans payable to affiliate	0		0		2,201
Other liabilities
Unearned affiliates insurance premiums and contract revenues	237		237		273
Accounts payable to affiliates	120		120		58
Notes payable to affiliate	51		51		61
Shareholder's Equity:
Dividends paid	744		744		741
Stock based compensation			$ 2		$ 2