Servicing Activities (Schedule of Total Serviced Automobile Loans Outstanding) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Automobile Serviced Assets [Line Items]
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	$ 51	$ 64	$ 45
Total Primary Serviced Assets	116,878	121,480
Consumer Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	67,631	65,646
Commercial Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	37,058	38,853
Operating Leases [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	8,682	11,311
Other Assets [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	121	67
Asset-backed Securities, Securitized Loans and Receivables [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	1,977	2,412
Whole-Loan Transactions [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	$ 1,409	$ 3,191