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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Residential Mortgage [Member]
Cash flows from sales of loans	$ 2,195	$ 890	$ 3,529	$ 1,606
Cash flows from repurchases of previously transferred loans	100	61	195	154
Cash flows from servicing fees	81	88	166	174
Cash flows from servicing advances recovered/(funded), net	7	11	19	28
Cash flows on mortgage-backed securities held	2,184	751	3,545	1,259
Carrying value of mortgage-backed securities held	22,400	17,500	22,400	17,500	$ 17,800
Commercial Mortgages [Member]
Cash flows from sales of loans	1,334	446	1,827	1,090
Cash flows from repurchases of previously transferred loans	10	4	25	4
Cash flows from servicing fees	31	32	64	63
Cash flows from servicing advances recovered/(funded), net	(140)	39	(128)	16
Cash flows on mortgage-backed securities held	14	15	51	29
Carrying value of mortgage-backed securities held	$ 900	$ 600	$ 900	$ 600	$ 600