AFS and HTM Debt Securities, Unrealized Loss Position, by Credit Rating (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale debt securities:
Gross unrealized losses	$ (573)	$ (4,218)
Available-for-sale, at fair value	265,983	269,912
Held-to-maturity debt securities:
Gross unrealized losses	(80)	(2,819)
Fair value	147,864	142,115
Total AFS and HTM debt securities:
Gross unrealized losses	(653)	(7,037)
Fair value	413,847	412,027
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	(17)	(106)
Available-for-sale, at fair value	15,319	13,348
Held-to-maturity debt securities:
Gross unrealized losses	(4)	(415)
Fair value	45,336	44,340
Securities of U.S. states and political subdivisions [Member]
Available-for-sale debt securities:
Gross unrealized losses	(78)	(446)
Available-for-sale, at fair value	45,095	49,264
Held-to-maturity debt securities:
Gross unrealized losses	(5)	(116)
Fair value	8,125	6,200
Mortgage-backed securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(314)	(3,167)
Available-for-sale, at fair value	161,301	160,203
Federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	(308)	(3,140)
Available-for-sale, at fair value	155,858	153,203
Held-to-maturity debt securities:
Gross unrealized losses	(71)	(2,288)
Fair value	94,346	91,509
Residential [Member]
Available-for-sale debt securities:
Gross unrealized losses	(1)	(5)
Available-for-sale, at fair value	1,263	2,775
Commercial [Member]
Available-for-sale debt securities:
Gross unrealized losses	(5)	(22)
Available-for-sale, at fair value	4,180	4,225
Corporate debt securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(36)	(90)
Available-for-sale, at fair value	6,230	6,271
Collateralized loan and other debt obligations [Member]
Available-for-sale debt securities:
Gross unrealized losses	(114)	(396)
Available-for-sale, at fair value	32,995	35,343
Held-to-maturity debt securities:
Gross unrealized losses	0	0
Fair value	57	66
Other [Member]
Available-for-sale debt securities:
Gross unrealized losses	(14)	(13)
Available-for-sale, at fair value	5,043	5,483
Unrated Investment Grade Securities [Member]
Total AFS and HTM debt securities:
Gross unrealized losses	(9)	(20)
Fair value	2,300	5,200
Investment grade [Member]
Available-for-sale debt securities:
Gross unrealized losses	(527)	(4,113)
Available-for-sale, at fair value	74,753	181,050
Held-to-maturity debt securities:
Gross unrealized losses	(79)	(2,809)
Fair value	19,501	128,545
Total AFS and HTM debt securities:
Gross unrealized losses	(606)	(6,922)
Fair value	94,254	309,595
Investment grade [Member] | Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	(17)	(106)
Available-for-sale, at fair value	11,291	6,702
Held-to-maturity debt securities:
Gross unrealized losses	(4)	(415)
Fair value	1,613	41,978
Investment grade [Member] | Securities of U.S. states and political subdivisions [Member]
Available-for-sale debt securities:
Gross unrealized losses	(69)	(425)
Available-for-sale, at fair value	7,480	18,447
Held-to-maturity debt securities:
Gross unrealized losses	(5)	(116)
Fair value	514	4,590
Investment grade [Member] | Mortgage-backed securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(313)	(3,162)
Available-for-sale, at fair value	34,477	125,525
Investment grade [Member] | Federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	(308)	(3,140)
Available-for-sale, at fair value	33,382	123,231
Held-to-maturity debt securities:
Gross unrealized losses	(70)	(2,278)
Fair value	17,374	81,977
Investment grade [Member] | Residential [Member]
Available-for-sale debt securities:
Gross unrealized losses	(1)	(2)
Available-for-sale, at fair value	180	295
Investment grade [Member] | Commercial [Member]
Available-for-sale debt securities:
Gross unrealized losses	(4)	(20)
Available-for-sale, at fair value	915	1,999
Investment grade [Member] | Corporate debt securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(6)	(17)
Available-for-sale, at fair value	299	791
Investment grade [Member] | Collateralized loan and other debt obligations [Member]
Available-for-sale debt securities:
Gross unrealized losses	(114)	(396)
Available-for-sale, at fair value	20,086	28,859
Held-to-maturity debt securities:
Gross unrealized losses	0	0
Fair value	0	0
Investment grade [Member] | Other [Member]
Available-for-sale debt securities:
Gross unrealized losses	(8)	(7)
Available-for-sale, at fair value	1,120	726
Non-investment grade [Member]
Available-for-sale debt securities:
Gross unrealized losses	(46)	(105)
Available-for-sale, at fair value	1,030	2,264
Held-to-maturity debt securities:
Gross unrealized losses	(1)	(10)
Fair value	33	399
Total AFS and HTM debt securities:
Gross unrealized losses	(47)	(115)
Fair value	1,063	2,663
Non-investment grade [Member] | Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	0	0
Available-for-sale, at fair value	0	0
Held-to-maturity debt 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 debt securities:
Gross unrealized losses	(9)	(21)
Available-for-sale, at fair value	219	316
Held-to-maturity debt securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Mortgage-backed securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(1)	(5)
Available-for-sale, at fair value	11	224
Non-investment grade [Member] | Federal agencies [Member]
Available-for-sale debt securities:
Gross unrealized losses	0	0
Available-for-sale, at fair value	0	0
Held-to-maturity debt securities:
Gross unrealized losses	(1)	(10)
Fair value	33	399
Non-investment grade [Member] | Residential [Member]
Available-for-sale debt securities:
Gross unrealized losses	0	(3)
Available-for-sale, at fair value	0	172
Non-investment grade [Member] | Commercial [Member]
Available-for-sale debt securities:
Gross unrealized losses	(1)	(2)
Available-for-sale, at fair value	11	52
Non-investment grade [Member] | Corporate debt securities [Member]
Available-for-sale debt securities:
Gross unrealized losses	(30)	(73)
Available-for-sale, at fair value	452	1,472
Non-investment grade [Member] | Collateralized loan and other debt obligations [Member]
Available-for-sale debt securities:
Gross unrealized losses	0	0
Available-for-sale, at fair value	0	0
Held-to-maturity debt securities:
Gross unrealized losses	0	0
Fair value	0	0
Non-investment grade [Member] | Other [Member]
Available-for-sale debt securities:
Gross unrealized losses	(6)	(6)
Available-for-sale, at fair value	$ 348	$ 252