Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Recurring - Level 3 - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 5,137	$ 5,395
Included in Earnings	497	(486)
Included in other comprehensive income	19	(256)
Purchases	249	132
Sales	(46)	(85)
Issuances	31	21
Settlements	(271)	159
Transfers into Level 3	3	4
Transfers out of Level 3	(8)	(11)
Ending Balance	5,611	4,873
Unrealized gains/losses on assets held on Consolidated Balance Sheet	487	(524)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	318	344
Included in Earnings	21	10
Purchases
Sales	2	1
Issuances	31	23
Settlements	(70)	(116)
Transfers into Level 3		2
Transfers out of Level 3		(2)
Ending Balance	302	262
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(26)	4
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	476	(496)
Net unrealized gains (losses) relating to Level 3 assets and liabilities	513	(528)
Loans held for sale | Residential mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	163	2
Included in Earnings	1
Purchases	35	2
Sales	(16)	(1)
Settlements	(16)
Transfers into Level 3	3	4
Transfers out of Level 3	(5)	(3)
Ending Balance	165	4
Loans held for sale | Commercial mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	57	64
Included in Earnings	(1)	(1)
Settlements		(3)
Ending Balance	56	60
Unrealized gains/losses on assets held on Consolidated Balance Sheet		(1)
Securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,647	2,055
Included in Earnings	10	18
Included in other comprehensive income	19	(256)
Purchases	1	4
Settlements	(84)	(104)
Ending Balance	1,593	1,717
Securities available for sale | Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,365	1,741
Included in Earnings	9	16
Included in other comprehensive income	16	(222)
Settlements	(74)	(93)
Ending Balance	1,316	1,442
Securities available for sale | Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	11
Ending Balance	11
Securities available for sale | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	199	240
Included in Earnings	1	2
Included in other comprehensive income	3	(29)
Settlements	(9)	(11)
Ending Balance	194	202
Securities available for sale | Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	72	74
Included in other comprehensive income		(5)
Purchases	1	4
Settlements	(1)
Ending Balance	72	73
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	647	300
Included in Earnings	10	11
Purchases	88	16
Sales	(3)	(26)
Issuances
Settlements	(28)	362
Transfers out of Level 3	(3)	(8)
Ending Balance	711	655
Unrealized gains/losses on assets held on Consolidated Balance Sheet	11	11
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,263	1,276
Included in Earnings	67	(69)
Purchases	40	71
Sales	(27)	(58)
Ending Balance	1,343	1,220
Unrealized gains/losses on assets held on Consolidated Balance Sheet	63	(64)
Mortgage Servicing Rights | Residential mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	673	995
Included in Earnings	295	(379)
Purchases	71	18
Issuances	13	10
Settlements	(73)	(39)
Ending Balance	979	605
Unrealized gains/losses on assets held on Consolidated Balance Sheet	295	(379)
Mortgage Servicing Rights | Commercial mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	569	649
Included in Earnings	129	(167)
Purchases	13	19
Issuances	18	11
Settlements	(28)	(35)
Ending Balance	701	477
Unrealized gains/losses on assets held on Consolidated Balance Sheet	129	(166)
Derivative
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	118	54
Included in Earnings	(14)	101
Purchases	1	2
Settlements	(42)	(22)
Ending Balance	63	135
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(11)	75
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	273	200
Included in Earnings	(14)	8
Sales	2	1
Settlements	(34)	(24)
Ending Balance	227	185
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(30)	10
Other borrowed funds
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	7
Issuances	1	12
Settlements	(1)	(14)
Ending Balance	2	5
Other liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	43	137
Included in Earnings	35	2
Issuances	30	11
Settlements	(35)	(78)
Transfers into Level 3		2
Transfers out of Level 3		(2)
Ending Balance	73	72
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	$ 4	$ (6)