Investment Securities - Investment Securities in an Unrealized Loss Position (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
AFS securities
AFS: Fair Value, Less than 12 Months	$ 2,810	$ 35,485
AFS: Fair Value, 12 Months or Longer	27,516	11,592
AFS: Fair Value, Total	30,326	47,077
AFS: Gross Unrealized Losses, Less than 12 Months	19	1,008
AFS: Gross Unrealized Losses, 12 Months or Longer	327	268
AFS: Gross Unrealized Losses, Total	346	1,276
HTM securities
HTM: Fair Value, Less than 12 Months		616
HTM: Fair Value, 12 Months or Longer		21,381
HTM: Fair Value, Total		21,997
HTM: Gross Unrealized Losses, Less than 12 Months		2
HTM: Gross Unrealized Losses, 12 Months or Longer		856
HTM: Gross Unrealized Losses, Total		858
Investment securities
Investment securities: Fair Value, Less than 12 Months	2,904	36,101
Investment securities: Fair Value, 12 Months or Longer	39,257	32,973
Investment securities: Fair Value	42,161	69,074
Investment securities: Gross Unrealized Loss, Less than 12 Months	19	1,010
Investment securities: Gross Unrealized Loss, 12 Months or Longer	482	1,124
Investment securities: Gross Unrealized Loss	501	2,134
U.S. Treasury and agency securities
AFS securities
AFS: Fair Value, Less than 12 Months	1,621	32,841
AFS: Fair Value, 12 Months or Longer	25,383	10,136
AFS: Fair Value, Total	27,004	42,977
AFS: Gross Unrealized Losses, Less than 12 Months	11	924
AFS: Gross Unrealized Losses, 12 Months or Longer	274	229
AFS: Gross Unrealized Losses, Total	285	1,153
HTM securities
HTM: Fair Value, Less than 12 Months	94	410
HTM: Fair Value, 12 Months or Longer	11,741	21,165
HTM: Fair Value, Total	11,835	21,575
HTM: Gross Unrealized Losses, Less than 12 Months	0	1
HTM: Gross Unrealized Losses, 12 Months or Longer	155	848
HTM: Gross Unrealized Losses, Total	155	849
U.S. Treasury securities
AFS securities
AFS: Fair Value, Less than 12 Months	0	19,937
AFS: Fair Value, 12 Months or Longer	14,432	5,994
AFS: Fair Value, Total	14,432	25,931
AFS: Gross Unrealized Losses, Less than 12 Months	0	541
AFS: Gross Unrealized Losses, 12 Months or Longer	159	115
AFS: Gross Unrealized Losses, Total	159	656
HTM securities
HTM: Fair Value, Less than 12 Months	0	0
HTM: Fair Value, 12 Months or Longer	4,804	11,161
HTM: Fair Value, Total	4,804	11,161
HTM: Gross Unrealized Losses, Less than 12 Months	0	0
HTM: Gross Unrealized Losses, 12 Months or Longer	69	403
HTM: Gross Unrealized Losses, Total	69	403
U.S. agency securities
AFS securities
AFS: Fair Value, Less than 12 Months	1,621	12,904
AFS: Fair Value, 12 Months or Longer	10,951	4,142
AFS: Fair Value, Total	12,572	17,046
AFS: Gross Unrealized Losses, Less than 12 Months	11	383
AFS: Gross Unrealized Losses, 12 Months or Longer	115	114
AFS: Gross Unrealized Losses, Total	126	497
HTM securities
HTM: Fair Value, Less than 12 Months	94	410
HTM: Fair Value, 12 Months or Longer	6,937	10,004
HTM: Fair Value, Total	7,031	10,414
HTM: Gross Unrealized Losses, Less than 12 Months	0	1
HTM: Gross Unrealized Losses, 12 Months or Longer	86	445
HTM: Gross Unrealized Losses, Total	86	446
Corporate and other debt
AFS securities
AFS: Fair Value, Less than 12 Months	1,189	2,644
AFS: Fair Value, 12 Months or Longer	2,133	1,456
AFS: Fair Value, Total	3,322	4,100
AFS: Gross Unrealized Losses, Less than 12 Months	8	84
AFS: Gross Unrealized Losses, 12 Months or Longer	53	39
AFS: Gross Unrealized Losses, Total	61	123
Agency CMBS
AFS securities
AFS: Fair Value, Less than 12 Months	320	808
AFS: Fair Value, 12 Months or Longer	750	0
AFS: Fair Value, Total	1,070	808
AFS: Gross Unrealized Losses, Less than 12 Months	1	62
AFS: Gross Unrealized Losses, 12 Months or Longer	36	0
AFS: Gross Unrealized Losses, Total	37	62
Non-agency CMBS
AFS securities
AFS: Fair Value, Less than 12 Months	0	0
AFS: Fair Value, 12 Months or Longer	218	446
AFS: Fair Value, Total	218	446
AFS: Gross Unrealized Losses, Less than 12 Months	0	0
AFS: Gross Unrealized Losses, 12 Months or Longer	2	14
AFS: Gross Unrealized Losses, Total	2	14
HTM securities
HTM: Fair Value, Less than 12 Months		206
HTM: Fair Value, 12 Months or Longer		216
HTM: Fair Value, Total		422
HTM: Gross Unrealized Losses, Less than 12 Months		1
HTM: Gross Unrealized Losses, 12 Months or Longer		8
HTM: Gross Unrealized Losses, Total		9
Corporate bonds
AFS securities
AFS: Fair Value, Less than 12 Months	349	470
AFS: Fair Value, 12 Months or Longer	403	1,010
AFS: Fair Value, Total	752	1,480
AFS: Gross Unrealized Losses, Less than 12 Months	2	7
AFS: Gross Unrealized Losses, 12 Months or Longer	3	25
AFS: Gross Unrealized Losses, Total	5	32
FFELP Student Loan ABS
AFS securities
AFS: Fair Value, Less than 12 Months	520	1,366
AFS: Fair Value, 12 Months or Longer	762	0
AFS: Fair Value, Total	1,282	1,366
AFS: Gross Unrealized Losses, Less than 12 Months	5	15
AFS: Gross Unrealized Losses, 12 Months or Longer	12	0
AFS: Gross Unrealized Losses, Total	$ 17	$ 15

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Amount of unrealized loss before deducting unrealized gain on investments securities that have been in a loss position for less than twelve months.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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