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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,474	$ 7,647	$ 6,475	$ 8,830
Included in earnings	176	109	543	374
Included in other comprehensive income	(3)	68	16	164
Purchases	163	167	478	486
Sales	(277)	(1,374)	(405)	(4,191)
Issuances	28	1,099	74	3,118
Settlements	(274)	(347)	(870)	(1,203)
Transfers Into Level 3	13	6	18	17
Transfers out of Level 3	(31)	(15)	(60)	(235)
Ending Balance	6,269	7,360	6,269	7,360
Unrealized gains/losses on assets held on Consolidated Balance Sheet	90	60	394	155
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	438	289	531	433
Included in earnings	30	19	12	56
Purchases			12
Sales	5	1	10	3
Issuances	76	32	142	216
Settlements	(143)	(50)	(301)	(417)
Ending Balance	406	291	406	291
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	32	17	13	60
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	146	90	531	318
Net unrealized gains (losses) relating to Level 3 assets and liabilities	58	43	381	95
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,804	3,403	3,080	3,723
Included in earnings	20	22	45	92
Included in other comprehensive income	(3)	68	16	164
Purchases	2	9	6	11
Sales		(8)		(46)
Settlements	(168)	(218)	(492)	(668)
Transfers out of Level 3	(5)		(5)
Ending Balance	2,650	3,276	2,650	3,276
Unrealized gains/losses on assets held on Consolidated Balance Sheet				(1)
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	282	290	298	335
Included in earnings	4	2	9	(3)
Purchases	25	20	80	60
Sales	(18)	(3)	(27)	(22)
Settlements	(1)	(14)	(44)	(51)
Transfers Into Level 3	8	5	8	11
Transfers out of Level 3	(19)	(9)	(43)	(39)
Ending Balance	281	291	281	291
Unrealized gains/losses on assets held on Consolidated Balance Sheet			1	(8)
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,167	987	1,036	1,331
Included in earnings	81	54	169	211
Purchases	52	103	213	184
Sales	(258)	(83)	(376)	(482)
Transfers out of Level 3				(183)
Ending Balance	1,042	1,061	1,042	1,061
Unrealized gains/losses on assets held on Consolidated Balance Sheet	18	38	77	127
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2	2	2
Ending Balance	2	2	2	2
Financial Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	16	22	10	40
Included in earnings	9	16	33	33
Purchases		1	2	3
Settlements	(17)	(17)	(37)	(54)
Ending Balance	8	22	8	22
Unrealized gains/losses on assets held on Consolidated Balance Sheet	11	22	37	58
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	384	248	487	414
Included in earnings	26	16	3	34
Sales	5	1	10	3
Settlements	(73)	(17)	(158)	(203)
Ending Balance	342	248	342	248
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	32	13	5	36
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	63	89	107	239
Included in earnings	(3)	5	(5)	10
Settlements	(2)		(44)	(155)
Ending Balance	58	94	58	94
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(3)	5	(5)	10
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7	8	11	10
Issuances	18	16	50	51
Settlements	(16)	(15)	(52)	(52)
Ending Balance	9	9	9	9
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	47	33	33	9
Included in earnings	4	3	9	22
Purchases			12
Issuances	58	16	92	165
Settlements	(54)	(18)	(91)	(162)
Ending Balance	55	34	55	34
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet		4	8	24
Other debt [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	91	78	87	66
Included in earnings			5
Included in other comprehensive income	1	3	8	15
Purchases	2	9	6	11
Sales		(7)		(8)
Settlements			(12)	(1)
Transfers out of Level 3	(5)		(5)
Ending Balance	89	83	89	83
Asset backed [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	308	361	332	403
Included in earnings	2	3	2	11
Included in other comprehensive income	(3)	4	1	19
Sales		(1)		(26)
Settlements	(14)	(19)	(42)	(59)
Ending Balance	293	348	293	348
Commercial Mortgage Backed Securities [Member] | Available-for-sale 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)
Residential Mortgage-backed Securities [Member] | Available-for-sale Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,405	2,964	2,661	3,254
Included in earnings	18	19	38	69
Included in other comprehensive income	(1)	61	7	130
Settlements	(154)	(199)	(438)	(608)
Ending Balance	2,268	2,845	2,268	2,845
Unrealized gains/losses on assets held on Consolidated Balance Sheet				(1)
Commercial Mortgages [Member] | Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	91	982	107	1,400
Included in earnings	1	14		51
Sales		(1,280)		(3,640)
Issuances		1,066		3,011
Settlements	(3)	(24)	(18)	(64)
Ending Balance	89	758	89	758
Unrealized gains/losses on assets held on Consolidated Balance Sheet		(2)		(13)
Commercial Mortgages [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	748	618	668	576
Included in earnings	23	6	104	20
Purchases	16	14	60	48
Issuances	16	19	39	65
Settlements	(37)	(29)	(105)	(81)
Ending Balance	766	628	766	628
Unrealized gains/losses on assets held on Consolidated Balance Sheet	23	6	104	19
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4	5	3	2
Purchases	2	2	4	8
Sales	(1)		(2)	(1)
Transfers Into Level 3	5	1	10	6
Transfers out of Level 3	(7)	(6)	(12)	(13)
Ending Balance	3	2	3	2
Residential Mortgage [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,297	1,249	1,164	1,182
Included in earnings	41	(10)	188	(40)
Purchases	66	18	113	172
Issuances	12	14	35	42
Settlements	(46)	(45)	(130)	(130)
Ending Balance	1,370	1,226	1,370	1,226
Unrealized gains/losses on assets held on Consolidated Balance Sheet	$ 41	$ (9)	$ 180	$ (37)