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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Residential Mortgage [Member]
Total principal balance	$ 51,821		$ 51,821		$ 54,028
Delinquent loans	572		572		622
Net charge-offs	13	$ 13	24	$ 25
Commercial Mortgages [Member]
Total principal balance	49,474		49,474		47,969
Delinquent loans	95		95		$ 234
Net charge-offs	$ 178	$ 22	$ 296	$ 52