Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Measurements, Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 7,647	$ 8,188	$ 8,830	$ 8,606
Included in earnings	109	166	374	(31)
Included in other comprehensive income	68	40	164	2
Purchases	167	113	486	416
Sales	(1,374)	(1,474)	(4,191)	(3,170)
Issuances	1,099	1,243	3,118	3,065
Settlements	(347)	(340)	(1,203)	(1,156)
Transfers Into Level 3	6	5	17	243
Transfers Out of Level 3	(15)	(12)	(235)	(46)
Ending Balance	7,360	7,929	7,360	7,929
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	60	114	155	(162)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	289	406	433	495
Included in earnings	19	21	56	91
Sales	1	1	3	4
Issuances	32	66	216	178
Settlements	(50)	(70)	(417)	(344)
Ending Balance	291	424	291	424
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	17	25	60	92
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	90	145	318	(122)
Net unrealized gains (losses) relating to Level 3 assets and liabilities	43	89	95	(254)
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5	6	2	5
Purchases	2	3	8	9
Sales		(1)	(1)	(2)
Transfers Into Level 3	1	3	6	8
Transfers Out of Level 3	(6)	(8)	(13)	(17)
Ending Balance	2	3	2	3
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	982	981	1,400	641
Included in earnings	14	18	51	55
Sales	(1,280)	(1,343)	(3,640)	(2,797)
Issuances	1,066	1,205	3,011	2,981
Settlements	(24)	(1)	(64)	(20)
Ending Balance	758	860	758	860
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(2)	6	(13)	4
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,403	4,041	3,723	4,535
Included in earnings	22	30	92	69
Included in other comprehensive income	68	40	164	4
Purchases	9	1	11	10
Sales	(8)	(14)	(46)	(78)
Settlements	(218)	(225)	(668)	(667)
Ending Balance	3,276	3,873	3,276	3,873
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet			(1)	(1)
Available-for-sale Securities [Member] | Residential mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,964	3,557	3,254	4,008
Included in earnings	19	25	69	58
Included in other comprehensive income	61	32	130	4
Sales				(60)
Settlements	(199)	(201)	(608)	(597)
Ending Balance	2,845	3,413	2,845	3,413
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet			(1)	(1)
Available-for-sale Securities [Member] | Commercial mortgage-backed securities [Member] | Mortgage-backed Securities Non-agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Included in earnings			12
Sales			(12)
Available-for-sale Securities [Member] | Asset backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	361	436	403	482
Included in earnings	3	4	11	10
Included in other comprehensive income	4	8	19
Sales	(1)		(26)
Settlements	(19)	(23)	(59)	(67)
Ending Balance	348	425	348	425
Available-for-sale Securities [Member] | Other debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	78	48	66	45
Included in earnings		1		1
Included in other comprehensive income	3		15
Purchases	9	1	11	10
Sales	(7)	(14)	(8)	(18)
Settlements		(1)	(1)	(3)
Ending Balance	83	35	83	35
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	290	317	335	340
Included in earnings	2	3	(3)	6
Purchases	20	27	60	82
Sales	(3)	(4)	(22)	(18)
Settlements	(14)	(15)	(51)	(57)
Transfers Into Level 3	5		11
Transfers Out of Level 3	(9)	(4)	(39)	(29)
Ending Balance	291	324	291	324
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet		1	(8)	3
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	987	1,353	1,331	1,098
Included in earnings	54	35	211	101
Purchases	103	17	184	135
Sales	(83)	(112)	(482)	(274)
Transfers Into Level 3		2		235
Transfers Out of Level 3			(183)
Ending Balance	1,061	1,295	1,061	1,295
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	38	30	127	93
Mortgage Servicing Rights [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,249	774	1,182	1,063
Included in earnings	(10)	23	(40)	(316)
Purchases	18	49	172	154
Issuances	14	16	42	39
Settlements	(45)	(42)	(130)	(120)
Ending Balance	1,226	820	1,226	820
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(9)	23	(37)	(308)
Mortgage Servicing Rights [Member] | Commercial Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	618	448	576	526
Included in earnings	6	8	20	(56)
Purchases	14	16	48	25
Issuances	19	22	65	45
Settlements	(29)	(21)	(81)	(67)
Ending Balance	628	473	628	473
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	6	8	19	(56)
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2	2	3
Settlements				(1)
Ending Balance	2	2	2	2
Financial Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	22	51	40	31
Included in earnings	16	37	33	106
Purchases	1		3	1
Settlements	(17)	(36)	(54)	(86)
Ending Balance	22	52	22	52
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	22	34	58	101
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	248	385	414	473
Included in earnings	16	21	34	90
Sales	1	1	3	4
Settlements	(17)	(13)	(203)	(173)
Ending Balance	248	394	248	394
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	13	25	36	92
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	89	215	239	364
Included in earnings	5	12	10	4
Included in other comprehensive income				(2)
Sales				(1)
Settlements			(155)	(138)
Ending Balance	94	227	94	227
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	5	12	10	2
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	8	8	10	12
Issuances	16	24	51	64
Settlements	(15)	(22)	(52)	(66)
Ending Balance	9	10	9	10
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	33	13	9	10
Included in earnings	3		22	1
Issuances	16	42	165	114
Settlements	(18)	(35)	(162)	(105)
Ending Balance	34	$ 20	34	$ 20
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	$ 4		$ 24