Loan Sale and Servicing Activities and Variable Interest Entities (Principal Balance, Delinquent Loans (Loans 90 Days or More Past Due), and Net Charge-Offs Related to Serviced Loans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Residential mortgage loans held for sale
Total principal balance	$ 41,096		$ 43,351
Delinquent loans	450		453
Net charge-offs	2	$ 8
Commercial mortgage loans held for sale
Total principal balance	41,735		40,790
Delinquent loans	126		$ 136
Net charge-offs	$ 153	$ 99