Securitizations and Variable Interest Entities (Schedule of Quantitative Information and Net Credit Losses about Securitized and Other Financial Assets Managed Together) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Loans managed and securitized, principal amount outstanding	$ 1,869	$ 3,363
Loans managed and securitized, delinquent amount at end of period	16	20
Loans managed and securitized, net credit losses	12	16
Off-balance sheet loans | Consumer portfolio segment | Automobile loan
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Loans managed and securitized, principal amount outstanding	1,235	1,964
Loans managed and securitized, delinquent amount at end of period	13	16
Loans managed and securitized, net credit losses	10	13
Whole-loan sales
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Loans managed and securitized, principal amount outstanding	634	1,399
Loans managed and securitized, delinquent amount at end of period	3	4
Loans managed and securitized, net credit losses	$ 2	$ 3