Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Measurements, Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,475	$ 8,830
Included in earnings	216	164
Included in other comprehensive income	9	31
Purchases	155	158
Sales	(23)	(1,822)
Issuances	30	847
Settlements	(305)	(487)
Transfers Into Level 3	4	4
Transfers out of Level 3	(15)	(199)
Ending Balance	6,546	7,526
Unrealized gains/losses on assets held on Consolidated Balance Sheet	192	112
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	531	433
Included in earnings	12	25
Purchases	12
Sales	3	2
Issuances	24	96
Settlements	(94)	(264)
Ending Balance	488	292
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	7	23
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	204	139
Net unrealized gains (losses) relating to Level 3 assets and liabilities	185	89
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,080	3,723
Included in earnings	23	30
Included in other comprehensive income	9	31
Purchases	2	1
Sales		(26)
Settlements	(154)	(222)
Ending Balance	2,960	3,537
Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	298	335
Included in earnings	2	1
Purchases	37	22
Sales	(7)	(4)
Settlements	(18)	(19)
Transfers Into Level 3	2	2
Transfers out of Level 3	(12)	(14)
Ending Balance	302	323
Unrealized gains/losses on assets held on Consolidated Balance Sheet	2
Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,036	1,331
Included in earnings	26	96
Purchases	82	37
Sales	(15)	(175)
Transfers out of Level 3		(183)
Ending Balance	1,129	1,106
Unrealized gains/losses on assets held on Consolidated Balance Sheet	25	67
Trading Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2
Ending Balance	2	2
Financial Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	10	40
Included in earnings	7	(1)
Purchases	1
Settlements	(6)	(15)
Ending Balance	12	24
Unrealized gains/losses on assets held on Consolidated Balance Sheet	9	22
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	487	414
Included in earnings	10	9
Sales	3	2
Settlements	(63)	(171)
Ending Balance	437	254
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	5	7
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	107	239
Included in earnings	3	(2)
Settlements	(42)	(155)
Ending Balance	68	82
Unrealized gains/losses on assets held on Consolidated Balance Sheet	3	(2)
Other Borrowed Funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	11	10
Issuances	19	19
Settlements	(21)	(22)
Ending Balance	9	7
Other liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	33	9
Included in earnings	2	16
Purchases	12
Issuances	5	77
Settlements	(10)	(71)
Ending Balance	42	31
Unrealized gains/losses on liabilities held on Consolidated Balance Sheet	2	16
Other debt [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	87	66
Included in earnings	5
Included in other comprehensive income	1	9
Purchases	2	1
Sales		(1)
Settlements	(1)
Ending Balance	94	75
Asset backed [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	332	403
Included in earnings	(1)	4
Included in other comprehensive income	5	4
Sales		(25)
Settlements	(15)	(20)
Ending Balance	321	366
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	2,661	3,254
Included in earnings	19	26
Included in other comprehensive income	3	18
Settlements	(138)	(202)
Ending Balance	2,545	3,096
Commercial Mortgages [Member] | Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	107	1,400
Included in earnings		9
Sales		(1,617)
Issuances		801
Settlements	(15)	(12)
Ending Balance	92	581
Unrealized gains/losses on assets held on Consolidated Balance Sheet		(5)
Commercial Mortgages [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	668	576
Included in earnings	48	13
Purchases	23	13
Issuances	17	29
Settlements	(33)	(25)
Ending Balance	723	606
Unrealized gains/losses on assets held on Consolidated Balance Sheet	48	13
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3	2
Purchases	1	2
Sales	(1)
Transfers Into Level 3	2	2
Transfers out of Level 3	(3)	(2)
Ending Balance	2	4
Residential Mortgage [Member] | Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,164	1,182
Included in earnings	107	18
Purchases	9	83
Issuances	13	17
Settlements	(37)	(39)
Ending Balance	1,256	1,261
Unrealized gains/losses on assets held on Consolidated Balance Sheet	$ 105	$ 17