Securitizations and Variable Interest Entities (Schedule of Cash Flow Received from and Paid to Nonconsolidated Securitization Entities) (Details) - Consumer Portfolio Segment [Member] - Automobile Loan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flow Received and Paid to Nonconsolidated Securitization Entities [Line Items]
Cash Flows Between Transferor and Transferee, Proceeds from New Transfers	$ 1,187	$ 1,715	$ 1,551
Cash Flows Between Transferor and Transferee, Purchases of Previously Transferred Financial Assets	(491)	0	0
Cash Flows Between Transferor and Transferee, Servicing Fees	31	35	28
Cash Flows Between Transferor and Transferee, Beneficial Interest	21	0	0
Cash Flows Between Transferor and Transferee, Receipts on Transferor's Interest in Transferred Financial Assets, Other	$ 4	$ 8	$ 0