Transfers of Receivables - Financial Performance Related to Securitizations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Securitization Transactions [Line Items]
Interest expense	$ 597	$ 582	$ 599	$ 638	$ 654	$ 663	$ 673	$ 666	$ 2,416	$ 2,656	$ 2,730
Securitization Transactions [Member]
Securitization Transactions [Line Items]
Interest expense									630	595	640
Securitization Transactions [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization Transactions [Line Items]
Interest expense									541	504	563
Securitization Transactions [Member] | Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Securitization Transactions [Line Items]
Interest expense									$ 89	$ 91	$ 77