Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 7,382	$ 18,837
Less than 12 Months, Gross Unrealized Losses	(31)	(522)
12 Months or Longer, Fair Value	8,871	2,760
12 Months or Longer, Gross Unrealized Losses	(206)	(109)
Total Fair Value	16,253	21,597
Total Gross Unrealized Losses	(237)	(631)
U.S. Treasury and agency debt obligations
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,499
Less than 12 Months, Gross Unrealized Losses	(1)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total Fair Value	1,499
Total Gross Unrealized Losses	(1)
Corporate debt securities guaranteed by U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	113	1,143
Less than 12 Months, Gross Unrealized Losses	(2)	(47)
12 Months or Longer, Fair Value	557	46
12 Months or Longer, Gross Unrealized Losses	(18)	(2)
Total Fair Value	670	1,189
Total Gross Unrealized Losses	(20)	(49)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	4,329	10,223
Less than 12 Months, Gross Unrealized Losses	(24)	(273)
12 Months or Longer, Fair Value	4,503	1,826
12 Months or Longer, Gross Unrealized Losses	(94)	(74)
Total Fair Value	8,832	12,049
Total Gross Unrealized Losses	(118)	(347)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3,917	9,769
Less than 12 Months, Gross Unrealized Losses	(15)	(263)
12 Months or Longer, Fair Value	4,413	1,770
12 Months or Longer, Gross Unrealized Losses	(90)	(69)
Total Fair Value	8,330	11,539
Total Gross Unrealized Losses	(105)	(332)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	412	454
Less than 12 Months, Gross Unrealized Losses	(9)	(10)
12 Months or Longer, Fair Value	90	56
12 Months or Longer, Gross Unrealized Losses	(4)	(5)
Total Fair Value	502	510
Total Gross Unrealized Losses	(13)	(15)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	552	3,794
Less than 12 Months, Gross Unrealized Losses	(3)	(117)
12 Months or Longer, Fair Value	2,674	439
12 Months or Longer, Gross Unrealized Losses	(72)	(27)
Total Fair Value	3,226	4,233
Total Gross Unrealized Losses	(75)	(144)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	294	2,842
Less than 12 Months, Gross Unrealized Losses	(2)	(74)
12 Months or Longer, Fair Value	1,993	256
12 Months or Longer, Gross Unrealized Losses	(58)	(10)
Total Fair Value	2,287	3,098
Total Gross Unrealized Losses	(60)	(84)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	258	952
Less than 12 Months, Gross Unrealized Losses	(1)	(43)
12 Months or Longer, Fair Value	681	183
12 Months or Longer, Gross Unrealized Losses	(14)	(17)
Total Fair Value	939	1,135
Total Gross Unrealized Losses	(15)	(60)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	783	2,528
Less than 12 Months, Gross Unrealized Losses	(1)	(34)
12 Months or Longer, Fair Value	586	392
12 Months or Longer, Gross Unrealized Losses	(9)	(2)
Total Fair Value	1,369	2,920
Total Gross Unrealized Losses	(10)	(36)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	106	1,149
Less than 12 Months, Gross Unrealized Losses	0	(51)
12 Months or Longer, Fair Value	551	57
12 Months or Longer, Gross Unrealized Losses	(13)	(4)
Total Fair Value	657	1,206
Total Gross Unrealized Losses	$ (13)	$ (55)