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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 5,827	$ 6,546	$ 6,157	$ 6,475
Included in earnings	(136)	151	(162)	367
Included in other comprehensive income	22	10	26	19
Purchases	255	160	349	315
Sales	(59)	(105)	(198)	(128)
Issuances	15	16	29	46
Settlements	(228)	(291)	(499)	(596)
Transfers Into Level 3	2	1	7	5
Transfers out of Level 3	(11)	(14)	(22)	(29)
Ending Balance	5,687	6,474	5,687	6,474
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(161)	114	(355)	306
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	298	488	333	531
Included in earnings	31	(30)	70	(18)
Purchases				12
Sales	1	2	3	5
Issuances	63	42	79	66
Settlements	(89)	(64)	(181)	(158)
Ending Balance	304	438	304	438
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	22	28	(64)	21
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	(167)	181	(232)	385
Net unrealized gains (losses) relating to Level 3 assets and liabilities	(183)	142	(419)	327
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2	2	3
Purchases	1	1	2	2
Sales			(1)	(1)
Transfers Into Level 3	1	3	4	5
Transfers out of Level 3	(2)	(2)	(5)	(5)
Ending Balance	2	4	2	4
Loans Held For Sale [Member] | Commercial Mortgages [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	73	92	87	107
Included in earnings	1	(1)	2	(1)
Settlements	(1)		(16)	(15)
Ending Balance	73	91	73	91
Unrealized gains/losses on assets held on Consolidated Balance Sheet	1	(1)	2	(1)
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,393	2,960	2,486	3,080
Included in earnings	20	2	38	25
Included in other comprehensive income	22	10	26	19
Purchases	2	2	3	4
Sales	(3)		(3)
Settlements	(117)	(170)	(233)	(324)
Ending Balance	2,317	2,804	2,317	2,804
Available-for-sale Securities [Member] | Asset backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	266	321	274	332
Included in earnings	2	1	2
Included in other comprehensive income	4	(1)	6	4
Settlements	(11)	(13)	(21)	(28)
Ending Balance	261	308	261	308
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	2,042	2,545	2,128	2,661
Included in earnings	18	1	36	20
Included in other comprehensive income	19	5	21	8
Settlements	(103)	(146)	(209)	(284)
Ending Balance	1,976	2,405	1,976	2,405
Available-for-sale Securities [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	85	94	84	87
Included in earnings				5
Included in other comprehensive income	(1)	6	(1)	7
Purchases	2	2	3	4
Sales	(3)		(3)
Settlements	(3)	(11)	(3)	(12)
Ending Balance	80	91	80	91
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	272	302	272	298
Included in earnings	2	3	5	5
Purchases	13	18	33	55
Sales	(8)	(2)	(11)	(9)
Issuances	(1)		(1)
Settlements	(11)	(25)	(25)	(43)
Transfers Into Level 3	1	(2)	3
Transfers out of Level 3	(9)	(12)	(17)	(24)
Ending Balance	259	282	259	282
Unrealized gains/losses on assets held on Consolidated Balance Sheet	1	(1)	2	1
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,217	1,129	1,255	1,036
Included in earnings	4	62	56	88
Purchases	150	79	195	161
Sales	(48)	(103)	(183)	(118)
Ending Balance	1,323	1,167	1,323	1,167
Unrealized gains/losses on assets held on Consolidated Balance Sheet	3	35	3	60
Mortgage Servicing Rights [Member] | Residential Mortgage [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,131	1,256	1,257	1,164
Included in earnings	(156)	40	(262)	147
Purchases	59	38	65	47
Issuances	7	10	14	23
Settlements	(44)	(47)	(77)	(84)
Ending Balance	997	1,297	997	1,297
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(156)	35	(261)	140
Mortgage Servicing Rights [Member] | Commercial Mortgages [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	681	723	726	668
Included in earnings	(55)	33	(88)	81
Purchases	32	21	51	44
Issuances	9	6	16	23
Settlements	(37)	(35)	(75)	(68)
Ending Balance	630	748	630	748
Unrealized gains/losses on assets held on Consolidated Balance Sheet	(55)	33	(88)	81
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2	2	2
Settlements	(2)		(2)
Ending Balance		2		2
Financial Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	56	12	25	10
Included in earnings	48	17	87	24
Purchases	(2)	1		2
Settlements	(16)	(14)	(26)	(20)
Ending Balance	86	16	86	16
Unrealized gains/losses on assets held on Consolidated Balance Sheet	45	18	(13)	27
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	230	437	268	487
Included in earnings	20	(33)	50	(23)
Sales	(1)	2	1	5
Settlements	(28)	(22)	(98)	(85)
Ending Balance	221	384	221	384
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	19	31	(53)	26
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		68	45	107
Included in earnings		(5)		(2)
Settlements			(45)	(42)
Ending Balance		63		63
Unrealized gains/losses on assets held on Consolidated Balance Sheet		(5)		(2)
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6	9	7	11
Issuances	12	13	26	32
Settlements	(13)	(15)	(28)	(36)
Ending Balance	5	7	5	7
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	62	42	58	33
Included in earnings	11	3	20	5
Purchases				12
Sales	2		2
Issuances	51	29	53	34
Settlements	(48)	(27)	(55)	(37)
Ending Balance	78	47	78	47
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	$ 3	$ (3)	$ (11)	$ (5)