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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Residential mortgage loans held for sale
Total principal balance	$ 44,345		$ 44,345		$ 43,351
Delinquent loans	548		548		453
Net charge-offs	1	$ 2	3	$ 10
Commercial mortgage loans held for sale
Total principal balance	41,036		41,036		40,790
Delinquent loans	62		62		$ 136
Net charge-offs	$ 25		$ 178	$ 99