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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Residential Mortgage [Member]
Total principal balance	$ 59,580		$ 59,580		$ 66,081
Delinquent loans	909		909		1,422
Net charge-offs	13	$ 24	62	$ 78
Commercial Mortgages [Member]
Total principal balance	47,376		47,376		45,855
Delinquent loans	566		566		$ 941
Net charge-offs	$ 228	$ 168	$ 639	$ 1,237