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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Residential Mortgage [Member]
Total principal balance	$ 50,786		$ 50,786		$ 54,028
Delinquent loans	529		529		622
Net charge-offs	8	$ 9	32	$ 34
Commercial Mortgages [Member]
Total principal balance	50,723		50,723		47,969
Delinquent loans	64		64		$ 234
Net charge-offs	$ 52	$ 117	$ 348	$ 169