Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Measurements, Recurring - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 8,830	$ 8,606
Included in earnings	446	536
Included in other comprehensive income	178	39
Purchases	589	643
Sales	(5,943)	(4,330)
Issuances	5,028	4,638
Settlements	(1,698)	(1,487)
Transfers Into Level 3	23	262
Transfers Out of Level 3	(978)	(77)
Ending Balance	6,475	8,830
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	198	323
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	433	495
Included in earnings	318	118
Sales	3	4
Issuances	245	219
Settlements	(466)	(403)
Transfer out of Level 3	(2)
Ending Balance	531	433
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	323	129
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	128	418
Net unrealized gains (losses) relating to Level 3 assets and liabilities	(125)	194
Loans Held For Sale | Residential Mortgage
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	5
Purchases	8	10
Sales	(1)	(3)
Transfers Into Level 3	10	10
Transfers Out of Level 3	(16)	(20)
Ending Balance	3	2
Loans Held For Sale | Commercial Mortgage
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,400	641
Included in earnings	81	79
Sales	(5,278)	(3,810)
Issuances	4,885	4,515
Settlements	(258)	(25)
Transfers Out of Level 3	(723)
Ending Balance	107	1,400
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	4	(3)
Available-for-sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,723	4,535
Included in earnings	101	89
Included in other comprehensive income	178	41
Purchases	13	12
Sales	(71)	(77)
Settlements	(864)	(877)
Transfers Into Level 3		2
Transfers Out of Level 3		(2)
Ending Balance	3,080	3,723
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(1)	(2)
Available-for-sale Securities | Residential mortgage-backed Securities | Mortgage-backed Securities Non-agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,254	4,008
Included in earnings	77	75
Included in other comprehensive income	137	16
Sales	(33)	(60)
Settlements	(774)	(785)
Ending Balance	2,661	3,254
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(1)	(2)
Available-for-sale Securities | Commercial Mortgage Backed Securities | Mortgage-backed Securities Non-agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Included in earnings	12
Sales	(12)
Available-for-sale Securities | Asset backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	403	482
Included in earnings	12	13
Included in other comprehensive income	22	(3)
Sales	(25)
Settlements	(80)	(89)
Ending Balance	332	403
Available-for-sale Securities | Other debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	66	45
Included in earnings		1
Included in other comprehensive income	19	28
Purchases	13	12
Sales	(1)	(17)
Settlements	(10)	(3)
Transfers Into Level 3		2
Transfers Out of Level 3		(2)
Ending Balance	87	66
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	335	340
Included in earnings		8
Purchases	97	126
Sales	(28)	(22)
Settlements	(68)	(78)
Transfers Into Level 3	13	15
Transfers Out of Level 3	(51)	(54)
Ending Balance	298	335
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(7)	2
Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,331	1,098
Included in earnings	239	148
Purchases	214	269
Sales	(565)	(418)
Transfers Into Level 3		235
Transfers Out of Level 3	(183)	(1)
Ending Balance	1,036	1,331
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	145	127
Mortgage Servicing Rights | Residential Mortgage
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,182	1,063
Included in earnings	(83)	37
Purchases	185	188
Issuances	55	62
Settlements	(175)	(168)
Ending Balance	1,164	1,182
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	(79)	39
Mortgage Servicing Rights | Commercial Mortgage
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	576	526
Included in earnings	46	45
Purchases	69	36
Issuances	88	61
Settlements	(111)	(92)
Ending Balance	668	576
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	45	45
Trading Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	3
Settlements		(1)
Ending Balance	2	2
Financial Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	40	31
Included in earnings	39	115
Purchases	3	2
Settlements	(67)	(108)
Transfers Out of Level 3	(5)
Ending Balance	10	40
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	67	102
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	414	473
Included in earnings	293	127
Sales	3	4
Settlements	(221)	(190)
Transfer out of Level 3	(2)
Ending Balance	487	414
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	297	129
Other Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	239	364
Included in earnings	23	15
Included in other comprehensive income		(2)
Sales
Settlements	(155)	(138)
Ending Balance	107	239
Unrealized gains or (losses) on assets held on Consolidated Balance Sheet	24	13
Other Borrowed Funds
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	10	12
Issuances	72	87
Settlements	(71)	(89)
Ending Balance	11	10
Other Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9	10
Included in earnings	25	(9)
Issuances	173	132
Settlements	(174)	(124)
Ending Balance	33	$ 9
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	$ 26