Transfers of Receivables - Derivative Income and Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative expense/(income) related to securitization transactions [Abstract]
Derivative expense/(income)	$ (227)	$ (939)	$ (481)
Securitization Transactions [Member]
Derivative expense/(income) related to securitization transactions [Abstract]
Derivative expense/(income)	(60)	29	(2)
Securitization Transactions [Member] | Related to Variable Interest Entity - Not VIE [Member]
Derivative expense/(income) related to securitization transactions [Abstract]
Derivative expense/(income)	(6)	(4)	12
Securitization Transactions [Member] | Other, Not Variable Interest Entity Related [Member]
Derivative expense/(income) related to securitization transactions [Abstract]
Derivative expense/(income)	(16)	10	18
Securitization Transactions [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivative expense/(income) related to securitization transactions [Abstract]
Derivative expense/(income)	$ (38)	$ 23	$ (32)