Investment Securities (Schedule of Investment Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
HTM securities:
HTM - Fair Value, Less than 12 Months	$ 1,921
HTM - Fair Value, 12 Months or Longer	0
HTM - Fair Value, Total	1,921
HTM - Gross Unrealized Losses, Less than 12 Months	8
HTM - Gross Unrealized Losses, 12 Months or Longer	0
HTM - Gross Unrealized Losses, Total	8
Investment securities - Fair Value, Less than 12 Months	17,418	$ 19,370
Investment securities - Fair Value, 12 Months or Longer	6,223	14,984
Investment securities - Fair Value	23,641	34,354
Investment securities - Gross Unrealized Loss, Less than 12 Months	121	44
Investment securities - Gross Unrealized Loss, 12 Months or Longer	141	236
Investment securities - Gross Unrealized Loss	262	280
U.S. Agency Securities
HTM securities:
HTM - Fair Value, Less than 12 Months	1,921
HTM - Fair Value, 12 Months or Longer	0
HTM - Fair Value, Total	1,921
HTM - Gross Unrealized Losses, Less than 12 Months	8
HTM - Gross Unrealized Losses, 12 Months or Longer	0
HTM - Gross Unrealized Losses, Total	8
AFS securities
Investment Securities
AFS - Fair Value, Less than 12 Months	15,497
AFS - Fair Value, 12 Months or Longer	6,223
AFS - Fair Value, Total	21,720
AFS - Gross Unrealized Losses, Less than 12 Months	113
AFS - Gross Unrealized Losses, 12 Months or Longer	141
AFS - Gross Unrealized Losses, Total	254
AFS Debt Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	15,485	19,359
AFS - Fair Value, 12 Months or Longer	6,223	14,984
AFS - Fair Value, Total	21,708	34,343
AFS - Gross Unrealized Losses, Less than 12 Months	110	40
AFS - Gross Unrealized Losses, 12 Months or Longer	141	236
AFS - Gross Unrealized Losses, Total	251	276
AFS Debt Securities \| U.S. Government and Agency Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	10,063	14,149
AFS - Fair Value, 12 Months or Longer	1,943	10,057
AFS - Fair Value, Total	12,006	24,206
AFS - Gross Unrealized Losses, Less than 12 Months	34	20
AFS - Gross Unrealized Losses, 12 Months or Longer	37	119
AFS - Gross Unrealized Losses, Total	71	139
AFS Debt Securities \| U.S. Treasury Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	1,926	11,410
AFS - Fair Value, 12 Months or Longer	0	5,924
AFS - Fair Value, Total	1,926	17,334
AFS - Gross Unrealized Losses, Less than 12 Months	3	14
AFS - Gross Unrealized Losses, 12 Months or Longer	0	53
AFS - Gross Unrealized Losses, Total	3	67
AFS Debt Securities \| U.S. Agency Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	8,137	2,739
AFS - Fair Value, 12 Months or Longer	1,943	4,133
AFS - Fair Value, Total	10,080	6,872
AFS - Gross Unrealized Losses, Less than 12 Months	31	6
AFS - Gross Unrealized Losses, 12 Months or Longer	37	66
AFS - Gross Unrealized Losses, Total	68	72
AFS Debt Securities \| Corporate and Other Debt
Investment Securities
AFS - Fair Value, Less than 12 Months	5,422	5,210
AFS - Fair Value, 12 Months or Longer	4,280	4,927
AFS - Fair Value, Total	9,702	10,137
AFS - Gross Unrealized Losses, Less than 12 Months	76	20
AFS - Gross Unrealized Losses, 12 Months or Longer	104	117
AFS - Gross Unrealized Losses, Total	180	137
AFS Debt Securities \| Agency
Investment Securities
AFS - Fair Value, Less than 12 Months	43	42
AFS - Fair Value, 12 Months or Longer	1,250	1,822
AFS - Fair Value, Total	1,293	1,864
AFS - Gross Unrealized Losses, Less than 12 Months	0	0
AFS - Gross Unrealized Losses, 12 Months or Longer	44	76
AFS - Gross Unrealized Losses, Total	44	76
AFS Debt Securities \| Non-Agency
Investment Securities
AFS - Fair Value, Less than 12 Months	634	706
AFS - Fair Value, 12 Months or Longer	475	346
AFS - Fair Value, Total	1,109	1,052
AFS - Gross Unrealized Losses, Less than 12 Months	6	3
AFS - Gross Unrealized Losses, 12 Months or Longer	6	3
AFS - Gross Unrealized Losses, Total	12	6
AFS Debt Securities \| Auto Loan Asset-backed Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	782	2,034
AFS - Fair Value, 12 Months or Longer	309	0
AFS - Fair Value, Total	1,091	2,034
AFS - Gross Unrealized Losses, Less than 12 Months	0	5
AFS - Gross Unrealized Losses, 12 Months or Longer	1	0
AFS - Gross Unrealized Losses, Total	1	5
AFS Debt Securities \| Corporate Bonds
Investment Securities
AFS - Fair Value, Less than 12 Months	1,196	905
AFS - Fair Value, 12 Months or Longer	469	1,299
AFS - Fair Value, Total	1,665	2,204
AFS - Gross Unrealized Losses, Less than 12 Months	8	6
AFS - Gross Unrealized Losses, 12 Months or Longer	9	16
AFS - Gross Unrealized Losses, Total	17	22
AFS Debt Securities \| Collateralized Loan Obligations
Investment Securities
AFS - Fair Value, Less than 12 Months	0	0
AFS - Fair Value, 12 Months or Longer	900	1,067
AFS - Fair Value, Total	900	1,067
AFS - Gross Unrealized Losses, Less than 12 Months	0	0
AFS - Gross Unrealized Losses, 12 Months or Longer	13	20
AFS - Gross Unrealized Losses, Total	13	20
AFS Debt Securities \| FFELP Student Loan Asset-backed Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	2,767	1,523
AFS - Fair Value, 12 Months or Longer	877	393
AFS - Fair Value, Total	3,644	1,916
AFS - Gross Unrealized Losses, Less than 12 Months	62	6
AFS - Gross Unrealized Losses, 12 Months or Longer	31	2
AFS - Gross Unrealized Losses, Total	93	8
AFS Equity Securities
Investment Securities
AFS - Fair Value, Less than 12 Months	12	11
AFS - Fair Value, 12 Months or Longer	0	0
AFS - Fair Value, Total	12	11
AFS - Gross Unrealized Losses, Less than 12 Months	3	4
AFS - Gross Unrealized Losses, 12 Months or Longer	0	0
AFS - Gross Unrealized Losses, Total	$ 3	$ 4

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