Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 4,938	$ 5,687	$ 5,395	$ 6,157
Included in earnings	157	(42)	(364)	(204)
Included in other comprehensive income	15	(6)	(100)	20
Purchases	200	220	485	569
Sales	(60)	(53)	(168)	(251)
Issuances	32	23	99	52
Settlements	(255)	(271)	(337)	(770)
Transfers Into Level 3	3	10	109	17
Transfers out of Level 3	(10)	(18)	(99)	(40)
Ending Balance	5,020	5,550	5,020	5,550
Unrealized gains/losses on assets held on Consolidated Balance Sheet	149	(65)	(402)	(318)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	296	304	344	333
Included in earnings	(3)	22	39	92
Purchases		16		16
Sales	1	4	3	7
Issuances	19	26	81	105
Settlements	(78)	(55)	(234)	(236)
Transfers into Level 3			2
Ending Balance	235	317	235	317
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(1)	21	28	85
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	160	(64)	(403)	(296)
Net unrealized gains (losses) relating to Level 3 assets and liabilities	150	(86)	(430)	(403)
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	88	2	2	2
Purchases	15	3	22	5
Sales	(10)		(12)	(1)
Settlements	(9)	(1)	(12)	(1)
Transfers Into Level 3	3	8	90	12
Transfers out of Level 3	(10)	(8)	(13)	(13)
Ending Balance	77	4	77	4
Loans Held For Sale [Member] | Commercial Mortgages [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	60	73	64	87
Included in earnings	(1)		(2)	2
Settlements		(1)	(3)	(17)
Ending Balance	59	72	59	72
Unrealized gains/losses on assets held on Consolidated Balance Sheet			(1)	2
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,792	2,317	2,055	2,486
Included in earnings	13	26	45	64
Included in other comprehensive income	15	(6)	(100)	20
Purchases	(1)	6	3	9
Sales				(3)
Settlements	(91)	(161)	(294)	(394)
Transfers Into Level 3			19
Ending Balance	1,728	2,182	1,728	2,182
Available-for-sale Securities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,491	1,976	1,741	2,128
Included in earnings	12	23	40	59
Included in other comprehensive income	18	(3)	(81)	18
Settlements	(83)	(143)	(262)	(352)
Ending Balance	1,438	1,853	1,438	1,853
Available-for-sale Securities [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19
Included in other comprehensive income	(8)		(8)
Transfers Into Level 3			19
Ending Balance	11		11
Available-for-sale Securities [Member] | Asset backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	210	261	240	274
Included in earnings	1	2	5	4
Included in other comprehensive income	5		(8)	6
Purchases		1		1
Settlements	(8)	(12)	(29)	(33)
Ending Balance	208	252	208	252
Available-for-sale Securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	72	80	74	84
Included in earnings		1		1
Included in other comprehensive income		(3)	(3)	(4)
Purchases	(1)	5	3	8
Sales				(3)
Settlements		(6)	(3)	(9)
Ending Balance	71	77	71	77
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	607	259	300	272
Included in earnings	7	5	20	10
Purchases	63	93	134	126
Sales	(3)	(7)	(34)	(18)
Issuances		1
Settlements	(27)	(14)	313	(39)
Transfers Into Level 3		2		5
Transfers out of Level 3		(10)	(86)	(27)
Ending Balance	647	329	647	329
Unrealized gains/losses on assets held on Consolidated Balance Sheet	7	4	20	6
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,183	1,323	1,276	1,255
Included in earnings	63	48	(68)	104
Purchases	60	65	173	260
Sales	(47)	(46)	(122)	(229)
Ending Balance	1,259	1,390	1,259	1,390
Unrealized gains/losses on assets held on Consolidated Balance Sheet	56	50	(69)	53
Mortgage Servicing Rights [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	577	997	995	1,257
Included in earnings	11	(100)	(408)	(362)
Purchases	52	22	113	87
Issuances	12	9	34	23
Settlements	(54)	(40)	(136)	(117)
Ending Balance	598	888	598	888
Unrealized gains/losses on assets held on Consolidated Balance Sheet	11	(97)	(408)	(353)
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	490	630	649	726
Included in earnings	23	(38)	(143)	(126)
Purchases	8	25	31	76
Issuances	20	13	65	29
Settlements	(26)	(35)	(87)	(110)
Ending Balance	515	595	515	595
Unrealized gains/losses on assets held on Consolidated Balance Sheet	23	(38)	(144)	(126)
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				2
Settlements				(2)
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	141	86	54	25
Included in earnings	41	17	192	104
Purchases	3	6	9	6
Settlements	(48)	(19)	(118)	(45)
Ending Balance	137	90	137	90
Unrealized gains/losses on assets held on Consolidated Balance Sheet	52	16	200	100
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	209	221	200	268
Included in earnings	(10)	8	26	58
Sales	1	4	3	5
Settlements	(57)	(27)	(86)	(125)
Ending Balance	143	206	143	206
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(7)	13	30	65
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance				45
Settlements				(45)
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	5	7	7
Issuances	2	13	27	39
Settlements	(2)	(12)	(32)	(40)
Ending Balance	2	6	2	6
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	85	78	137	58
Included in earnings	7	14	13	34
Purchases		16		16
Sales				2
Issuances	17	13	54	66
Settlements	(19)	(16)	(116)	(71)
Transfers into Level 3			2
Ending Balance	90	105	90	105
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	$ 6	$ 8	$ (2)	$ 20