Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 18,642	$ 7,382
Less than 12 Months, Gross Unrealized Losses	(156)	(31)
12 Months or Longer, Fair Value	6,328	8,871
12 Months or Longer, Gross Unrealized Losses	(165)	(206)
Total Fair Value	24,970	16,253
Total Gross Unrealized Losses	(321)	(237)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3,096	1,499
Less than 12 Months, Gross Unrealized Losses	(9)	(1)
12 Months or Longer, Fair Value	1	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	3,097	1,499
Total Gross Unrealized Losses	(9)	(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
Less than 12 Months, Gross Unrealized Losses		(2)
12 Months or Longer, Fair Value		557
12 Months or Longer, Gross Unrealized Losses		(18)
Total Fair Value		670
Total Gross Unrealized Losses		(20)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	12,380	4,329
Less than 12 Months, Gross Unrealized Losses	(120)	(24)
12 Months or Longer, Fair Value	4,575	4,503
12 Months or Longer, Gross Unrealized Losses	(114)	(94)
Total Fair Value	16,955	8,832
Total Gross Unrealized Losses	(234)	(118)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	12,025	3,917
Less than 12 Months, Gross Unrealized Losses	(110)	(15)
12 Months or Longer, Fair Value	4,420	4,413
12 Months or Longer, Gross Unrealized Losses	(102)	(90)
Total Fair Value	16,445	8,330
Total Gross Unrealized Losses	(212)	(105)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	355	412
Less than 12 Months, Gross Unrealized Losses	(10)	(9)
12 Months or Longer, Fair Value	155	90
12 Months or Longer, Gross Unrealized Losses	(12)	(4)
Total Fair Value	510	502
Total Gross Unrealized Losses	(22)	(13)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,091	552
Less than 12 Months, Gross Unrealized Losses	(22)	(3)
12 Months or Longer, Fair Value	1,478	2,674
12 Months or Longer, Gross Unrealized Losses	(49)	(72)
Total Fair Value	3,569	3,226
Total Gross Unrealized Losses	(71)	(75)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,352	294
Less than 12 Months, Gross Unrealized Losses	(9)	(2)
12 Months or Longer, Fair Value	1,148	1,993
12 Months or Longer, Gross Unrealized Losses	(38)	(58)
Total Fair Value	2,500	2,287
Total Gross Unrealized Losses	(47)	(60)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	739	258
Less than 12 Months, Gross Unrealized Losses	(13)	(1)
12 Months or Longer, Fair Value	330	681
12 Months or Longer, Gross Unrealized Losses	(11)	(14)
Total Fair Value	1,069	939
Total Gross Unrealized Losses	(24)	(15)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	825	783
Less than 12 Months, Gross Unrealized Losses	(5)	(1)
12 Months or Longer, Fair Value	255	586
12 Months or Longer, Gross Unrealized Losses	(1)	(9)
Total Fair Value	1,080	1,369
Total Gross Unrealized Losses	(6)	(10)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	250	106
Less than 12 Months, Gross Unrealized Losses	0	0
12 Months or Longer, Fair Value	19	551
12 Months or Longer, Gross Unrealized Losses	(1)	(13)
Total Fair Value	269	657
Total Gross Unrealized Losses	$ (1)	$ (13)