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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Residential mortgage loans held for sale
Total principal balance	$ 43,447		$ 43,447		$ 43,351
Delinquent loans	551		551		453
Net charge-offs	1	$ 4	4	$ 14
Commercial mortgage loans held for sale
Total principal balance	40,775		40,775		40,790
Delinquent loans	71		71		$ 136
Net charge-offs	$ 2	$ 4	$ 180	$ 103