Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Measurements, Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,546	$ 7,526	$ 6,475	$ 8,830
Included in earnings	151	101	367	265
Included in other comprehensive income	10	65	19	96
Purchases	160	161	315	319
Sales	(105)	(995)	(128)	(2,817)
Issuances	16	1,172	46	2,019
Settlements	(291)	(369)	(596)	(856)
Transfers Into Level 3	1	7	5	11
Transfers out of Level 3	(14)	(21)	(29)	(220)
Ending Balance	6,474	7,647	6,474	7,647
Unrealized gains/losses on assets held on Consolidated Balance Sheet	114	(4)	306	92
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	488	292	531	433
Included in earnings	(30)	12	(18)	37
Purchases			12
Sales	2		5	2
Issuances	42	88	66	184
Settlements	(64)	(103)	(158)	(367)
Ending Balance	438	289	438	289
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(28)	15	(21)	53
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	181	89	385	228
Net unrealized gains (losses) relating to Level 3 assets and liabilities	142	(19)	327	39
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,960	3,537	3,080	3,723
Included in earnings	2	40	25	70
Included in other comprehensive income	10	65	19	96
Purchases	2	1	4	2
Sales		(12)		(38)
Settlements	(170)	(228)	(324)	(450)
Ending Balance	2,804	3,403	2,804	3,403
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	302	323	298	335
Included in earnings	3	(6)	5	(5)
Purchases	18	18	55	40
Sales	(2)	(15)	(9)	(19)
Settlements	(25)	(18)	(43)	(37)
Transfers Into Level 3	(2)	4		6
Transfers out of Level 3	(12)	(16)	(24)	(30)
Ending Balance	282	290	282	290
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(1)	(8)	1	(7)
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,129	1,106	1,036	1,331
Included in earnings	62	61	88	157
Purchases	79	44	161	81
Sales	(103)	(224)	(118)	(399)
Transfers out of Level 3				(183)
Ending Balance	1,167	987	1,167	987
Unrealized gains/losses on assets held on Consolidated Balance Sheet	35	22	60	88
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	12	24	10	40
Included in earnings	17	18	24	17
Purchases	1	2	2	2
Settlements	(14)	(22)	(20)	(37)
Ending Balance	16	22	16	22
Unrealized gains/losses on assets held on Consolidated Balance Sheet	18	16	27	35
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	437	254	487	414
Included in earnings	(33)	9	(23)	18
Sales	2		5	2
Settlements	(22)	(15)	(85)	(186)
Ending Balance	384	248	384	248
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	(31)	12	(26)	34
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	68	82	107	239
Included in earnings	(5)	7	(2)	5
Settlements			(42)	(155)
Ending Balance	63	89	63	89
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(5)	8	(2)	6
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9	7	11	10
Issuances	13	16	32	35
Settlements	(15)	(15)	(36)	(37)
Ending Balance	7	8	7	8
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	42	31	33	9
Included in earnings	3	3	5	19
Purchases			12
Issuances	29	72	34	149
Settlements	(27)	(73)	(37)	(144)
Ending Balance	47	33	47	33
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	3	3	5	19
Other debt [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	94	75	87	66
Included in earnings			5
Included in other comprehensive income	6	3	7	12
Purchases	2	1	4	2
Sales				(1)
Settlements	(11)	(1)	(12)	(1)
Ending Balance	91	78	91	78
Asset backed [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	321	366	332	403
Included in earnings	1	4		8
Included in other comprehensive income	(1)	11	4	15
Sales				(25)
Settlements	(13)	(20)	(28)	(40)
Ending Balance	308	361	308	361
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		12
Sales		(12)		(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	2,545	3,096	2,661	3,254
Included in earnings	1	24	20	50
Included in other comprehensive income	5	51	8	69
Settlements	(146)	(207)	(284)	(409)
Ending Balance	2,405	2,964	2,405	2,964
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	92	581	107	1,400
Included in earnings	(1)	28	(1)	37
Sales		(743)		(2,360)
Issuances		1,144		1,945
Settlements		(28)	(15)	(40)
Ending Balance	91	982	91	982
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(1)		(1)
Commercial Mortgages [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	723	606	668	576
Included in earnings	33	1	81	14
Purchases	21	21	44	34
Issuances	6	17	23	46
Settlements	(35)	(27)	(68)	(52)
Ending Balance	748	618	748	618
Unrealized gains/losses on assets held on Consolidated Balance Sheet	33		81
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	4	3	2
Purchases	1	4	2	6
Sales		(1)	(1)	(1)
Transfers Into Level 3	3	3	5	5
Transfers out of Level 3	(2)	(5)	(5)	(7)
Ending Balance	4	5	4	5
Residential Mortgage [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,256	1,261	1,164	1,182
Included in earnings	40	(48)	147	(30)
Purchases	38	71	47	154
Issuances	10	11	23	28
Settlements	(47)	(46)	(84)	(85)
Ending Balance	1,297	1,249	1,297	1,249
Unrealized gains/losses on assets held on Consolidated Balance Sheet	$ 35	$ (42)	$ 140	$ (29)