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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Residential Mortgage
Total principal balance	$ 54,028	$ 58,320
Delinquent loans	622	899
Net charge-offs	47	78
Commercial Mortgages
Total principal balance	47,969	49,116
Delinquent loans	234	355
Net charge-offs	$ 269	$ 965