AFS and HTM Debt Securities, Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	$ (117)	$ (598)
Less than 12 months, Fair value, available-for-sale	27,542	54,683
12 months or more, Gross unrealized losses, available-for-sale	(456)	(3,620)
12 months or more, Fair value, available-for-sale	48,241	128,631
Total, Gross unrealized losses, available-for-sale	(573)	(4,218)
Total Fair Value, available for sale	75,783	183,314
Held-to-maturity debt securities:
Less than 12 months, Gross unrealized losses, held-to-maturity	(1)	(12)
Less than 12 months, Fair value, held-to-maturity	15	6,128
12 months or more, Gross unrealized losses, held-to-maturity	(79)	(2,807)
12 months or more, Fair value, held-to-maturity	19,519	122,816
Total, Gross unrealized losses, held-to-maturity	(80)	(2,819)
Total, Fair value, held-to-maturity	19,534	128,944
Total AFS and HTM debt securities:
Less than 12 months, Gross unrealized losses, investment securities	(118)	(610)
Less than 12 months, Fair value, investment securities	27,557	60,811
12 months or more, Gross unrealized losses, investment securities	(535)	(6,427)
12 months or more, Fair value, investment securities	67,760	251,447
Total, Gross unrealized losses, investment securities	(653)	(7,037)
Total, Fair value, investment securities	95,317	312,258
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(2)	(1)
Less than 12 months, Fair value, available-for-sale	5,780	498
12 months or more, Gross unrealized losses, available-for-sale	(15)	(105)
12 months or more, Fair value, available-for-sale	5,511	6,204
Total, Gross unrealized losses, available-for-sale	(17)	(106)
Total Fair Value, available for sale	11,291	6,702
Held-to-maturity debt securities:
Less than 12 months, Gross unrealized losses, held-to-maturity	0	(3)
Less than 12 months, Fair value, held-to-maturity	0	895
12 months or more, Gross unrealized losses, held-to-maturity	(4)	(412)
12 months or more, Fair value, held-to-maturity	1,613	41,083
Total, Gross unrealized losses, held-to-maturity	(4)	(415)
Total, Fair value, held-to-maturity	1,613	41,978
Securities of U.S. states and political subdivisions [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(32)	(73)
Less than 12 months, Fair value, available-for-sale	5,003	9,746
12 months or more, Gross unrealized losses, available-for-sale	(46)	(373)
12 months or more, Fair value, available-for-sale	2,696	9,017
Total, Gross unrealized losses, available-for-sale	(78)	(446)
Total Fair Value, available for sale	7,699	18,763
Held-to-maturity debt securities:
Less than 12 months, Gross unrealized losses, held-to-maturity	0	(4)
Less than 12 months, Fair value, held-to-maturity	0	598
12 months or more, Gross unrealized losses, held-to-maturity	(5)	(112)
12 months or more, Fair value, held-to-maturity	514	3,992
Total, Gross unrealized losses, held-to-maturity	(5)	(116)
Total, Fair value, held-to-maturity	514	4,590
Mortgage-backed securities [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(6)	(65)
Less than 12 months, Fair value, available-for-sale	2,220	13,349
12 months or more, Gross unrealized losses, available-for-sale	(308)	(3,102)
12 months or more, Fair value, available-for-sale	32,268	112,400
Total, Gross unrealized losses, available-for-sale	(314)	(3,167)
Total Fair Value, available for sale	34,488	125,749
Federal agencies [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(2)	(42)
Less than 12 months, Fair value, available-for-sale	1,203	10,979
12 months or more, Gross unrealized losses, available-for-sale	(306)	(3,098)
12 months or more, Fair value, available-for-sale	32,179	112,252
Total, Gross unrealized losses, available-for-sale	(308)	(3,140)
Total Fair Value, available for sale	33,382	123,231
Held-to-maturity debt securities:
Less than 12 months, Gross unrealized losses, held-to-maturity	(1)	(5)
Less than 12 months, Fair value, held-to-maturity	15	4,635
12 months or more, Gross unrealized losses, held-to-maturity	(70)	(2,283)
12 months or more, Fair value, held-to-maturity	17,392	77,741
Total, Gross unrealized losses, held-to-maturity	(71)	(2,288)
Total, Fair value, held-to-maturity	17,407	82,376
Residential [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(1)	(3)
Less than 12 months, Fair value, available-for-sale	180	398
12 months or more, Gross unrealized losses, available-for-sale	0	(2)
12 months or more, Fair value, available-for-sale	0	69
Total, Gross unrealized losses, available-for-sale	(1)	(5)
Total Fair Value, available for sale	180	467
Commercial [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(3)	(20)
Less than 12 months, Fair value, available-for-sale	837	1,972
12 months or more, Gross unrealized losses, available-for-sale	(2)	(2)
12 months or more, Fair value, available-for-sale	89	79
Total, Gross unrealized losses, available-for-sale	(5)	(22)
Total Fair Value, available for sale	926	2,051
Corporate debt securities [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(11)	(64)
Less than 12 months, Fair value, available-for-sale	470	1,965
12 months or more, Gross unrealized losses, available-for-sale	(25)	(26)
12 months or more, Fair value, available-for-sale	281	298
Total, Gross unrealized losses, available-for-sale	(36)	(90)
Total Fair Value, available for sale	751	2,263
Collateralized loan and other debt obligations [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(58)	(388)
Less than 12 months, Fair value, available-for-sale	12,847	28,306
12 months or more, Gross unrealized losses, available-for-sale	(56)	(8)
12 months or more, Fair value, available-for-sale	7,239	553
Total, Gross unrealized losses, available-for-sale	(114)	(396)
Total Fair Value, available for sale	20,086	28,859
Held-to-maturity debt securities:
Less than 12 months, Gross unrealized losses, held-to-maturity	0	0
Less than 12 months, Fair value, held-to-maturity	0	0
12 months or more, Gross unrealized losses, held-to-maturity	0	0
12 months or more, Fair value, held-to-maturity	0	0
Total, Gross unrealized losses, held-to-maturity	0	0
Total, Fair value, held-to-maturity	0	0
Other [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(8)	(7)
Less than 12 months, Fair value, available-for-sale	1,222	819
12 months or more, Gross unrealized losses, available-for-sale	(6)	(6)
12 months or more, Fair value, available-for-sale	246	159
Total, Gross unrealized losses, available-for-sale	(14)	(13)
Total Fair Value, available for sale	$ 1,468	$ 978