Loan Sale and Servicing Activities and Variable Interest Entities (Cash Flows Associated with Loan Sale and Servicing Activities) (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]
Cash flows from sales of loans	$ 890	$ 1,051	$ 1,606	$ 2,244
Cash flows from repurchases of previously transferred loans	61	77	154	196
Cash flows from servicing fees	88	89	174	181
Cash flows from servicing advances recovered (funded), net	11	39	28	43
Cash flows on mortgage-backed securities held	751	449	1,259	871
Carrying value of mortgage-backed securities held	17,500	12,400	17,500	12,400	$ 13,300
Commercial Mortgages [Member]
Cash flows from sales of loans	446	458	1,090	1,660
Cash flows from repurchases of previously transferred loans	4		4
Cash flows from servicing fees	32	35	63	66
Cash flows from servicing advances recovered (funded), net	39	(12)	16	5
Cash flows on mortgage-backed securities held	15	28	29	49
Carrying value of mortgage-backed securities held	$ 600	$ 700	$ 600	$ 700	$ 600