Transfers of Receivables - Financial Performance Related to Securitizations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Securitization Transactions [Line Items]
Interest expense	$ 691	$ 741	$ 2,056	$ 2,318
Securitization Transactions [Member]
Securitization Transactions [Line Items]
Interest expense	157	194	488	672
Securitization Transactions [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization Transactions [Line Items]
Interest expense	138	171	434	599
Securitization Transactions [Member] | Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Securitization Transactions [Line Items]
Interest expense	$ 19	$ 23	$ 54	$ 73