Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Recurring - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 5,611	$ 4,873	$ 5,137	$ 5,395
Included in Earnings	78	(35)	575	(521)
Included in other comprehensive income	3	141	22	(115)
Purchases	417	153	666	285
Sales	(97)	(23)	(143)	(108)
Issuances	45	46	76	67
Settlements	(318)	(241)	(589)	(82)
Transfers into Level 3	5	102	8	106
Transfers out of Level 3	(10)	(78)	(18)	(89)
Impact from BBVA Acquisition	571		571
Ending Balance	6,305	4,938	6,305	4,938
Unrealized gains/losses on assets held on Consolidated Balance Sheet	44	(16)	531	(541)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	302	262	318	344
Included in Earnings	32	32	53	42
Purchases
Sales	1	1	3	2
Issuances	287	39	318	62
Settlements	(303)	(40)	(373)	(156)
Transfers into Level 3				2
Transfers out of Level 3		2
Impact from BBVA Acquisition	7		7
Ending Balance	326	296	326	296
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	46	25	20	29
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	46	(67)	522	(563)
Net unrealized gains (losses) relating to Level 3 assets and liabilities	(2)	(41)	511	(570)
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	165	4	163	2
Included in Earnings	(1)
Purchases	3	5	38	7
Sales	(36)	(1)	(52)	(2)
Settlements	(12)	(3)	(28)	(3)
Transfers into Level 3	5	83	8	87
Transfers out of Level 3	(5)		(10)	(3)
Ending Balance	119	88	119	88
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	56	60	57	64
Included in Earnings	1			(1)
Sales	(6)		(6)
Settlements	1		1	(3)
Ending Balance	52	60	52	60
Unrealized gains/losses on assets held on Consolidated Balance Sheet			1	(1)
Loans held for sale | Other consumer loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance
Impact from BBVA Acquisition	239		239
Ending Balance	239		239
Securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,593	1,717	1,647	2,055
Included in Earnings	11	14	21	32
Included in other comprehensive income	3	141	22	(115)
Purchases	2		3	4
Sales
Settlements	(113)	(99)	(197)	(203)
Transfers into Level 3		19		19
Ending Balance	1,496	1,792	1,496	1,792
Securities available for sale | Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,316	1,442	1,365	1,741
Included in Earnings	11	12	20	28
Included in other comprehensive income		123	16	(99)
Settlements	(90)	(86)	(164)	(179)
Ending Balance	1,237	1,491	1,237	1,491
Securities available for sale | Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	11		11
Transfers into Level 3		19		19
Ending Balance	11	19	11	19
Securities available for sale | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	194	202	199	240
Included in Earnings		2	1	4
Included in other comprehensive income	2	16	5	(13)
Purchases
Settlements	(21)	(10)	(30)	(21)
Ending Balance	175	210	175	210
Securities available for sale | Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	72	73	72	74
Included in Earnings
Included in other comprehensive income	1	2	1	(3)
Purchases	2		3	4
Settlements	(2)	(3)	(3)	(3)
Ending Balance	73	72	73	72
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	711	655	647	300
Included in Earnings	10	2	20	13
Purchases	9	55	97	71
Sales	(3)	(5)	(6)	(31)
Issuances
Settlements	(35)	(22)	(63)	340
Transfers out of Level 3	(5)	(78)	(8)	(86)
Impact from BBVA Acquisition	292		292
Ending Balance	979	607	979	607
Unrealized gains/losses on assets held on Consolidated Balance Sheet	10	2	20	13
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,343	1,220	1,263	1,276
Included in Earnings	157	(62)	224	(131)
Purchases	92	42	132	113
Sales	(52)	(17)	(79)	(75)
Impact from BBVA Acquisition
Ending Balance	1,540	1,183	1,540	1,183
Unrealized gains/losses on assets held on Consolidated Balance Sheet	136	(62)	199	(125)
Mortgage Servicing Rights | Residential mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	979	605	673	995
Included in Earnings	(141)	(40)	154	(419)
Purchases	301	43	372	61
Issuances	24	12	37	22
Settlements	(87)	(43)	(160)	(82)
Impact from BBVA Acquisition	35		35
Ending Balance	1,111	577	1,111	577
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(141)	(41)	154	(420)
Mortgage Servicing Rights | Commercial mortgage loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	701	477	569	649
Included in Earnings	(19)	1	110	(166)
Purchases	8	4	21	23
Issuances	21	34	39	45
Settlements	(29)	(26)	(57)	(61)
Impact from BBVA Acquisition
Ending Balance	682	490	682	490
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(18)	1	111	(166)
Financial derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	63	135	118	54
Included in Earnings	60	50	46	151
Purchases	2	4	3	6
Settlements	(43)	(48)	(85)	(70)
Impact from BBVA Acquisition	5		5
Ending Balance	87	141	87	141
Unrealized gains/losses on assets held on Consolidated Balance Sheet	57	84	46	158
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	227	185	273	200
Included in Earnings	4	28	(10)	36
Sales	1	1	3	2
Issuances
Settlements	(39)	(5)	(73)	(29)
Impact from BBVA Acquisition	7		7
Ending Balance	200	209	200	209
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	19	27	(11)	37
Other borrowed funds
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	5	2	7
Issuances		13	1	25
Settlements		(16)	(1)	(30)
Ending Balance	2	2	2	2
Other liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	73	72	43	137
Included in Earnings	28	4	63	6
Issuances	287	26	317	37
Settlements	(264)	(19)	(299)	(97)
Transfers into Level 3				2
Transfers out of Level 3		2
Ending Balance	124	85	124	85
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	$ 27	$ (2)	$ 31	$ (8)