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	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Loans managed and securitized, principal amount outstanding	$ 1,460		$ 1,869
Loans managed and securitized, delinquent amount at end of period	10		16
Loans managed and securitized, net credit losses	2	$ 4
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	957		1,235
Loans managed and securitized, delinquent amount at end of period	8		13
Loans managed and securitized, net credit losses	2	3
Whole-loan sales
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Loans managed and securitized, principal amount outstanding	503		634
Loans managed and securitized, delinquent amount at end of period	2		$ 3
Loans managed and securitized, net credit losses	$ 0	$ 1