Transfers of Receivables - Financial Performance Related to Securitizations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Securitization Transactions [Line Items]
Interest expense	$ 709	$ 741	$ 774	$ 803	$ 831	$ 888	$ 895	$ 893	$ 3,027	$ 3,507	$ 4,222
Securitization Transactions [Member]
Securitization Transactions [Line Items]
Interest expense									854	1,136	1,471
Securitization Transactions [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization Transactions [Line Items]
Interest expense									760	994	1,247
Securitization Transactions [Member] | Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Securitization Transactions [Line Items]
Interest expense									$ 94	$ 142	$ 224