Variable Interest Entities - Loans Sold to Third-Party Sponsored Securitization Entities (Details) - Nonconsolidated entities - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Summary of loan sale activities [Abstract]
Carrying value of loans sold	$ 35,556	$ 11,968	$ 73,873	$ 28,804
Proceeds received from loan sales as cash	3	1	73	1
Proceeds from loans sales as securities	35,512	11,713	73,172	28,291
Total proceeds received from loan sales	35,515	11,714	73,245	28,292
Gains on loan sales	$ 342	$ 9	$ 495	$ 32