Servicing Activities (Schedule of Total Serviced Automobile Loans Outstanding) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Automobile Serviced Assets [Line Items]
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	$ 8	$ 16
Total Primary Serviced Assets	117,134		$ 116,878
Consumer Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	68,738		67,631
Commercial Loan [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	36,935		37,058
Operating Leases [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	8,489		8,682
Other Assets [Member] | On-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	131		121
Asset-backed Securities, Securitized Loans and Receivables [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	1,666		1,977
Whole-Loan Transactions [Member] | Off-Balance Sheet Loans [Member]
Automobile Serviced Assets [Line Items]
Total Primary Serviced Assets	$ 1,175		$ 1,409