Investment Securities, Unrealized Loss Position, by Credit Rating (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale securities:
Gross unrealized losses	$ (2,580)	$ (5,407)
Fair value	269,202	308,364
Held-to-maturity securities:
Gross unrealized losses	(896)	(1,027)
Fair value	140,390	99,155
Total investment securities:
Gross unrealized losses	(3,476)	(6,434)
Fair value	409,592	407,519
Total debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(2,573)	(5,396)
Fair value	268,174	307,153
Held-to-maturity securities:
Fair value	140,390	99,155
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	(65)	(109)
Fair value	17,896	25,819
Held-to-maturity securities:
Gross unrealized losses	(35)	(77)
Fair value	45,335	45,079
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Gross unrealized losses	(975)	(1,571)
Fair value	52,013	51,101
Held-to-maturity securities:
Gross unrealized losses	(55)	(144)
Fair value	6,330	6,209
Mortgage-backed securities: [Member]
Available-for-sale securities:
Gross unrealized losses	(1,425)	(3,540)
Fair value	148,710	177,548
Federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	(1,407)	(3,458)
Fair value	135,938	161,230
Held-to-maturity securities:
Gross unrealized losses	(806)	(804)
Fair value	86,881	44,457
Residential [Member]
Available-for-sale securities:
Gross unrealized losses	(2)	(8)
Fair value	7,359	7,816
Commercial [Member]
Available-for-sale securities:
Gross unrealized losses	(16)	(74)
Fair value	5,413	8,502
Corporate debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(83)	(110)
Fair value	9,602	11,457
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Gross unrealized losses	(11)	(31)
Fair value	33,455	35,020
Held-to-maturity securities:
Gross unrealized losses	0	(1)
Fair value	998	1,070
Other [Member]
Available-for-sale securities:
Gross unrealized losses	(14)	(35)
Fair value	6,498	6,208
Held-to-maturity securities:
Gross unrealized losses	0	(1)
Fair value	846	2,340
Total marketable equity securities [Member]
Available-for-sale securities:
Gross unrealized losses	(7)	(11)
Fair value	1,028	1,211
Perpetual preferred securities [Member]
Available-for-sale securities:
Gross unrealized losses	(4)	(11)
Fair value	465	469
Unrated Investment Grade Securities [Member]
Total investment securities:
Gross unrealized losses	(32)	(54)
Fair value	6,600	7,000
Investment grade [Member]
Available-for-sale securities:
Gross unrealized losses	(2,446)	(5,202)
Fair value	129,621	179,308
Held-to-maturity securities:
Gross unrealized losses	(895)	(1,026)
Fair value	70,046	52,199
Total investment securities:
Gross unrealized losses	(3,341)	(6,228)
Fair value	199,667	231,507
Investment grade [Member] | Total debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(2,443)	(5,192)
Fair value	129,558	179,240
Investment grade [Member] | Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	(65)	(109)
Fair value	11,486	10,816
Held-to-maturity securities:
Gross unrealized losses	(35)	(77)
Fair value	3,347	6,351
Investment grade [Member] | Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Gross unrealized losses	(932)	(1,517)
Fair value	27,640	33,271
Held-to-maturity securities:
Gross unrealized losses	(55)	(144)
Fair value	3,624	4,871
Investment grade [Member] | Mortgage-backed securities: [Member]
Available-for-sale securities:
Gross unrealized losses	(1,411)	(3,474)
Fair value	84,796	126,977
Investment grade [Member] | Federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	(1,407)	(3,458)
Fair value	84,014	124,216
Held-to-maturity securities:
Gross unrealized losses	(805)	(803)
Fair value	63,075	40,078
Investment grade [Member] | Residential [Member]
Available-for-sale securities:
Gross unrealized losses	(1)	(1)
Fair value	54	176
Investment grade [Member] | Commercial [Member]
Available-for-sale securities:
Gross unrealized losses	(3)	(15)
Fair value	728	2,585
Investment grade [Member] | Corporate debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(14)	(31)
Fair value	630	1,238
Investment grade [Member] | Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Gross unrealized losses	(11)	(31)
Fair value	4,009	5,096
Held-to-maturity securities:
Gross unrealized losses	0	(1)
Fair value	0	266
Investment grade [Member] | Other [Member]
Available-for-sale securities:
Gross unrealized losses	(10)	(30)
Fair value	997	1,842
Held-to-maturity securities:
Gross unrealized losses	0	(1)
Fair value	0	633
Investment grade [Member] | Perpetual preferred securities [Member]
Available-for-sale securities:
Gross unrealized losses	(3)	(10)
Fair value	63	68
Non-investment grade [Member]
Available-for-sale securities:
Gross unrealized losses	(131)	(205)
Fair value	1,930	2,860
Held-to-maturity securities:
Gross unrealized losses	(1)	(1)
Fair value	35	17
Total investment securities:
Gross unrealized losses	(132)	(206)
Fair value	1,965	2,877
Non-investment grade [Member] | Total debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(130)	(204)
Fair value	1,911	2,842
Non-investment grade [Member] | Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	0	0
Fair value	0	0
Held-to-maturity securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Gross unrealized losses	(43)	(54)
Fair value	372	354
Held-to-maturity securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Mortgage-backed securities: [Member]
Available-for-sale securities:
Gross unrealized losses	(14)	(66)
Fair value	425	1,160
Non-investment grade [Member] | Federal agencies [Member]
Available-for-sale securities:
Gross unrealized losses	0	0
Fair value	0	0
Held-to-maturity securities:
Gross unrealized losses	(1)	(1)
Fair value	35	17
Non-investment grade [Member] | Residential [Member]
Available-for-sale securities:
Gross unrealized losses	(1)	(7)
Fair value	114	596
Non-investment grade [Member] | Commercial [Member]
Available-for-sale securities:
Gross unrealized losses	(13)	(59)
Fair value	311	564
Non-investment grade [Member] | Corporate debt securities [Member]
Available-for-sale securities:
Gross unrealized losses	(69)	(79)
Fair value	690	937
Non-investment grade [Member] | Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Gross unrealized losses	0	0
Fair value	0	0
Held-to-maturity securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Other [Member]
Available-for-sale securities:
Gross unrealized losses	(4)	(5)
Fair value	424	391
Held-to-maturity securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Perpetual preferred securities [Member]
Available-for-sale securities:
Gross unrealized losses	(1)	(1)
Fair value	$ 19	$ 18