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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Residential Mortgage [Member]
Cash flows from sales of loans	$ 1,799	$ 1,296	$ 5,328	$ 2,902
Cash flows from repurchases of previously transferred loans	352	81	547	235
Cash flows from servicing fees	85	90	251	264
Cash flows from servicing advances recovered/(funded), net	(15)	5	4	33
Cash flows on mortgage-backed securities held	2,829	1,394	6,374	2,653
Carrying value of mortgage-backed securities held	19,500	17,700	19,500	17,700	$ 17,800
Commercial Mortgages [Member]
Cash flows from sales of loans	839	1,122	2,666	2,212
Cash flows from repurchases of previously transferred loans	107		132	4
Cash flows from servicing fees	33	34	97	97
Cash flows from servicing advances recovered/(funded), net	(78)	45	(206)	61
Cash flows on mortgage-backed securities held	14	14	65	43
Carrying value of mortgage-backed securities held	$ 800	$ 600	$ 800	$ 600	$ 600