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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Residential mortgage loans held for sale
Cash flows from sales of loans	$ 2,475	$ 1,799	$ 5,997	$ 5,328
Cash flows from repurchases of previously transferred loans	45	352	189	547
Cash flows from servicing fees	105	85	270	251
Cash flows from servicing advances recovered/(funded), net	(4)	(15)	8	4
Cash flows on mortgage-backed securities held	2,041	2,829	7,256	6,374
Carrying value of mortgage-backed securities held	15,900	19,500	15,900	19,500	$ 16,500
Commercial mortgage loans held for sale
Cash flows from sales of loans	881	839	2,604	2,666
Cash flows from repurchases of previously transferred loans	103	107	145	132
Cash flows from servicing fees	43	33	119	97
Cash flows from servicing advances recovered/(funded), net	28	(78)	(8)	(206)
Cash flows on mortgage-backed securities held	18	14	66	65
Carrying value of mortgage-backed securities held	$ 600	$ 800	$ 600	$ 800	$ 800