Investment Securities - Investment Securities in an Unrealized Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
AFS securities
AFS: Fair Value, Less than 12 Months	$ 9,101	$ 35,485
AFS: Fair Value, 12 Months or Longer	18,333	11,592
AFS: Fair Value, Total	27,434	47,077
AFS: Gross Unrealized Losses, Less than 12 Months	41	1,008
AFS: Gross Unrealized Losses, 12 Months or Longer	192	268
AFS: Gross Unrealized Losses, Total	233	1,276
HTM securities
HTM: Fair Value, Less than 12 Months	5,307	616
HTM: Fair Value, 12 Months or Longer	3,522	21,381
HTM: Fair Value, Total	8,829	21,997
HTM: Gross Unrealized Losses, Less than 12 Months	15	2
HTM: Gross Unrealized Losses, 12 Months or Longer	33	856
HTM: Gross Unrealized Losses, Total	48	858
Investment securities
Investment securities: Fair Value, Less than 12 Months	14,408	36,101
Investment securities: Fair Value, 12 Months or Longer	21,855	32,973
Investment securities: Fair Value	36,263	69,074
Investment securities: Gross Unrealized Loss, Less than 12 Months	56	1,010
Investment securities: Gross Unrealized Loss, 12 Months or Longer	225	1,124
Investment securities: Gross Unrealized Loss	281	2,134
U.S. Treasury and agency securities
AFS securities
AFS: Fair Value, Less than 12 Months	7,297	32,841
AFS: Fair Value, 12 Months or Longer	16,601	10,136
AFS: Fair Value, Total	23,898	42,977
AFS: Gross Unrealized Losses, Less than 12 Months	28	924
AFS: Gross Unrealized Losses, 12 Months or Longer	148	229
AFS: Gross Unrealized Losses, Total	176	1,153
HTM securities
HTM: Fair Value, Less than 12 Months	5,307	410
HTM: Fair Value, 12 Months or Longer	3,522	21,165
HTM: Fair Value, Total	8,829	21,575
HTM: Gross Unrealized Losses, Less than 12 Months	15	1
HTM: Gross Unrealized Losses, 12 Months or Longer	33	848
HTM: Gross Unrealized Losses, Total	48	849
U.S. Treasury securities
AFS securities
AFS: Fair Value, Less than 12 Months	4,233	19,937
AFS: Fair Value, 12 Months or Longer	9,318	5,994
AFS: Fair Value, Total	13,551	25,931
AFS: Gross Unrealized Losses, Less than 12 Months	13	541
AFS: Gross Unrealized Losses, 12 Months or Longer	75	115
AFS: Gross Unrealized Losses, Total	88	656
HTM securities
HTM: Fair Value, Less than 12 Months	2,811	0
HTM: Fair Value, 12 Months or Longer	950	11,161
HTM: Fair Value, Total	3,761	11,161
HTM: Gross Unrealized Losses, Less than 12 Months	8	0
HTM: Gross Unrealized Losses, 12 Months or Longer	2	403
HTM: Gross Unrealized Losses, Total	10	403
U.S. agency securities
AFS securities
AFS: Fair Value, Less than 12 Months	3,064	12,904
AFS: Fair Value, 12 Months or Longer	7,283	4,142
AFS: Fair Value, Total	10,347	17,046
AFS: Gross Unrealized Losses, Less than 12 Months	15	383
AFS: Gross Unrealized Losses, 12 Months or Longer	73	114
AFS: Gross Unrealized Losses, Total	88	497
HTM securities
HTM: Fair Value, Less than 12 Months	2,496	410
HTM: Fair Value, 12 Months or Longer	2,572	10,004
HTM: Fair Value, Total	5,068	10,414
HTM: Gross Unrealized Losses, Less than 12 Months	7	1
HTM: Gross Unrealized Losses, 12 Months or Longer	31	445
HTM: Gross Unrealized Losses, Total	38	446
Corporate and other debt
AFS securities
AFS: Fair Value, Less than 12 Months	1,804	2,644
AFS: Fair Value, 12 Months or Longer	1,732	1,456
AFS: Fair Value, Total	3,536	4,100
AFS: Gross Unrealized Losses, Less than 12 Months	13	84
AFS: Gross Unrealized Losses, 12 Months or Longer	44	39
AFS: Gross Unrealized Losses, Total	57	123
Agency CMBS
AFS securities
AFS: Fair Value, Less than 12 Months	837	808
AFS: Fair Value, 12 Months or Longer	719	0
AFS: Fair Value, Total	1,556	808
AFS: Gross Unrealized Losses, Less than 12 Months	6	62
AFS: Gross Unrealized Losses, 12 Months or Longer	30	0
AFS: Gross Unrealized Losses, Total	36	62
Non-agency CMBS
AFS securities
AFS: Fair Value, Less than 12 Months		0
AFS: Fair Value, 12 Months or Longer		446
AFS: Fair Value, Total		446
AFS: Gross Unrealized Losses, Less than 12 Months		0
AFS: Gross Unrealized Losses, 12 Months or Longer		14
AFS: Gross Unrealized Losses, Total		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	477	470
AFS: Fair Value, 12 Months or Longer	262	1,010
AFS: Fair Value, Total	739	1,480
AFS: Gross Unrealized Losses, Less than 12 Months	3	7
AFS: Gross Unrealized Losses, 12 Months or Longer	1	25
AFS: Gross Unrealized Losses, Total	4	32
FFELP Student Loan ABS
AFS securities
AFS: Fair Value, Less than 12 Months	490	1,366
AFS: Fair Value, 12 Months or Longer	751	0
AFS: Fair Value, Total	1,241	1,366
AFS: Gross Unrealized Losses, Less than 12 Months	4	15
AFS: Gross Unrealized Losses, 12 Months or Longer	13	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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