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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Residential Mortgage [Member]
Total principal balance	$ 47,765		$ 47,765		$ 49,323
Delinquent loans	433		433		492
Net charge-offs	2	$ 13	10	$ 24
Commercial Mortgages [Member]
Total principal balance	41,391		41,391		42,414
Delinquent loans	$ 100		100		$ 64
Net charge-offs		$ 178	$ 99	$ 296