Investment Securities (Investment Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investment securities
Investment securities: Fair Value, Less than 12 Months	$ 51,918	$ 46,712
Investment securities: Fair Value, 12 Months or Longer	18,608	19,563
Investment securities: Fair Value	70,526	66,275
Investment securities: Gross Unrealized Loss, Less than 12 Months	1,501	858
Investment securities: Gross Unrealized Loss, 12 Months or Longer	920	590
Investment securities: Gross Unrealized Loss	2,421	1,448
AFS Securities
AFS securities
AFS: Fair Value, Less than 12 Months	40,709	37,101
AFS: Fair Value, 12 Months or Longer	7,000	7,753
AFS: Fair Value, Total	47,709	44,854
AFS: Gross Unrealized Losses, Less than 12 Months	1,199	747
AFS: Gross Unrealized Losses, 12 Months or Longer	249	175
AFS: Gross Unrealized Losses, Total	1,448	922
AFS Debt Securities
AFS securities
AFS: Fair Value, Less than 12 Months		37,101
AFS: Fair Value, 12 Months or Longer		7,748
AFS: Fair Value, Total		44,849
AFS: Gross Unrealized Losses, Less than 12 Months		747
AFS: Gross Unrealized Losses, 12 Months or Longer		165
AFS: Gross Unrealized Losses, Total		912
AFS Debt Securities \| U.S. Government and Agency Securities
AFS securities
AFS: Fair Value, Less than 12 Months	37,675	34,614
AFS: Fair Value, 12 Months or Longer	6,375	6,800
AFS: Fair Value, Total	44,050	41,414
AFS: Gross Unrealized Losses, Less than 12 Months	1,113	687
AFS: Gross Unrealized Losses, 12 Months or Longer	224	149
AFS: Gross Unrealized Losses, Total	1,337	836
AFS Debt Securities \| U.S. Treasury Securities
AFS securities
AFS: Fair Value, Less than 12 Months	25,041	21,941
AFS: Fair Value, 12 Months or Longer	3,958	4,287
AFS: Fair Value, Total	28,999	26,228
AFS: Gross Unrealized Losses, Less than 12 Months	711	495
AFS: Gross Unrealized Losses, 12 Months or Longer	122	94
AFS: Gross Unrealized Losses, Total	833	589
AFS Debt Securities \| U.S. Agency Securities
AFS securities
AFS: Fair Value, Less than 12 Months	12,634	12,673
AFS: Fair Value, 12 Months or Longer	2,417	2,513
AFS: Fair Value, Total	15,051	15,186
AFS: Gross Unrealized Losses, Less than 12 Months	402	192
AFS: Gross Unrealized Losses, 12 Months or Longer	102	55
AFS: Gross Unrealized Losses, Total	504	247
AFS Debt Securities \| Corporate and Other Debt
AFS securities
AFS: Fair Value, Less than 12 Months	3,034	2,487
AFS: Fair Value, 12 Months or Longer	625	948
AFS: Fair Value, Total	3,659	3,435
AFS: Gross Unrealized Losses, Less than 12 Months	86	60
AFS: Gross Unrealized Losses, 12 Months or Longer	25	16
AFS: Gross Unrealized Losses, Total	111	76
AFS Debt Securities \| CMBS: Agency
AFS securities
AFS: Fair Value, Less than 12 Months	910	930
AFS: Fair Value, 12 Months or Longer	0	0
AFS: Fair Value, Total	910	930
AFS: Gross Unrealized Losses, Less than 12 Months	59	49
AFS: Gross Unrealized Losses, 12 Months or Longer	0	0
AFS: Gross Unrealized Losses, Total	59	49
AFS Debt Securities \| CMBS: Non-Agency
AFS securities
AFS: Fair Value, Less than 12 Months	309	257
AFS: Fair Value, 12 Months or Longer	242	559
AFS: Fair Value, Total	551	816
AFS: Gross Unrealized Losses, Less than 12 Months	7	1
AFS: Gross Unrealized Losses, 12 Months or Longer	10	7
AFS: Gross Unrealized Losses, Total	17	8
AFS Debt Securities \| Corporate Bonds
AFS securities
AFS: Fair Value, Less than 12 Months	809	316
AFS: Fair Value, 12 Months or Longer	383	389
AFS: Fair Value, Total	1,192	705
AFS: Gross Unrealized Losses, Less than 12 Months	13	3
AFS: Gross Unrealized Losses, 12 Months or Longer	15	9
AFS: Gross Unrealized Losses, Total	28	12
AFS Debt Securities \| FFELP Student Loan ABS
AFS securities
AFS: Fair Value, Less than 12 Months	1,006	984
AFS: Fair Value, 12 Months or Longer	0	0
AFS: Fair Value, Total	1,006	984
AFS: Gross Unrealized Losses, Less than 12 Months	7	7
AFS: Gross Unrealized Losses, 12 Months or Longer	0	0
AFS: Gross Unrealized Losses, Total	7	7
AFS Equity Securities
AFS securities
AFS: Fair Value, Less than 12 Months		0
AFS: Fair Value, 12 Months or Longer		5
AFS: Fair Value, Total		5
AFS: Gross Unrealized Losses, Less than 12 Months		0
AFS: Gross Unrealized Losses, 12 Months or Longer		10
AFS: Gross Unrealized Losses, Total		10
HTM securities
HTM securities
HTM: Fair Value, Less than 12 Months	11,209	9,611
HTM: Fair Value, 12 Months or Longer	11,608	11,810
HTM: Fair Value, Total	22,817	21,421
HTM: Gross Unrealized Losses, Less than 12 Months	302	111
HTM: Gross Unrealized Losses, 12 Months or Longer	671	415
HTM: Gross Unrealized Losses, Total	973	526
HTM securities \| U.S. Government and Agency Securities
HTM securities
HTM: Fair Value, Less than 12 Months	10,989	9,487
HTM: Fair Value, 12 Months or Longer	11,608	11,810
HTM: Fair Value, Total	22,597	21,297
HTM: Gross Unrealized Losses, Less than 12 Months	296	110
HTM: Gross Unrealized Losses, 12 Months or Longer	671	415
HTM: Gross Unrealized Losses, Total	967	525
HTM securities \| U.S. Treasury Securities
HTM securities
HTM: Fair Value, Less than 12 Months	6,585	6,608
HTM: Fair Value, 12 Months or Longer	4,742	4,512
HTM: Fair Value, Total	11,327	11,120
HTM: Gross Unrealized Losses, Less than 12 Months	177	86
HTM: Gross Unrealized Losses, 12 Months or Longer	313	219
HTM: Gross Unrealized Losses, Total	490	305
HTM securities \| U.S. Agency Securities
HTM securities
HTM: Fair Value, Less than 12 Months	4,404	2,879
HTM: Fair Value, 12 Months or Longer	6,866	7,298
HTM: Fair Value, Total	11,270	10,177
HTM: Gross Unrealized Losses, Less than 12 Months	119	24
HTM: Gross Unrealized Losses, 12 Months or Longer	358	196
HTM: Gross Unrealized Losses, Total	477	220
HTM securities \| Corporate and Other Debt
HTM securities
HTM: Fair Value, Less than 12 Months	220	124
HTM: Fair Value, 12 Months or Longer	0	0
HTM: Fair Value, Total	220	124
HTM: Gross Unrealized Losses, Less than 12 Months	6	1
HTM: Gross Unrealized Losses, 12 Months or Longer	0	0
HTM: Gross Unrealized Losses, Total	6	1
HTM securities \| CMBS: Non-Agency
HTM securities
HTM: Fair Value, Less than 12 Months	220	124
HTM: Fair Value, 12 Months or Longer	0	0
HTM: Fair Value, Total	220	124
HTM: Gross Unrealized Losses, Less than 12 Months	6	1
HTM: Gross Unrealized Losses, 12 Months or Longer	0	0
HTM: Gross Unrealized Losses, Total	$ 6	$ 1

Amount of unrealized loss on investments securities that have been in a loss position for twelve months or longer.

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Amount of unrealized loss on investments securities.

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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 accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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