Variable Interest Entities - Securitization Activity (Details) - Securitization entities not consolidated - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Residential mortgage
Securitization activity [Abstract]
Principal securitized	$ 6,431	$ 5,532	$ 1,817
All cash flows during the period:
Proceeds received from loan sales as financial instruments	6,449	5,661	1,831
Servicing fees collected	319	338	477
Purchases of previously transferred financial assets (or the underlying collateral)	0	1	37
Cash flows received on interests	$ 411	$ 463	$ 482
Weighted-average life (in years)	7 years 7 months 6 days	4 years 9 months 18 days	4 years 6 months
Weighted-average discount rate	3.60%	2.90%	4.20%
Commercial and other
Securitization activity [Abstract]
Principal securitized	$ 10,159	$ 10,252	$ 8,964
All cash flows during the period:
Proceeds received from loan sales as financial instruments	10,218	10,340	9,094
Servicing fees collected	2	3	3
Purchases of previously transferred financial assets (or the underlying collateral)	0	0	0
Cash flows received on interests	$ 301	$ 918	$ 1,441
Weighted-average life (in years)	5 years 3 months 18 days	7 years 1 month 6 days	6 years 2 months 12 days
Weighted-average discount rate	4.00%	4.40%	5.80%