Transfers of Receivables - Exposure Based on Fair Value of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	$ 935	$ 909
Fair Value of Derivative Liabilities	310	166
Securitization Transactions [Member]
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	121	57
Fair Value of Derivative Liabilities	31	27
Related to Variable Interest Entity - Not VIE [Member] | Securitization Transactions [Member]
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	23	11
Fair Value of Derivative Liabilities	29	21
Other, Not Variable Interest Entity Related [Member] | Securitization Transactions [Member]
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	34	21
Fair Value of Derivative Liabilities	0	1
Variable Interest Entity, Primary Beneficiary [Member]
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	64	25
Fair Value of Derivative Liabilities	2	5
Variable Interest Entity, Primary Beneficiary [Member] | Securitization Transactions [Member]
Securitization Transactions [Line Items]
Fair Value of Derivative Assets	64	25
Fair Value of Derivative Liabilities	$ 2	$ 5