Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 21,141	$ 18,642
Less than 12 Months, Gross Unrealized Losses	(419)	(156)
12 Months or Longer, Fair Value	5,905	6,328
12 Months or Longer, Gross Unrealized Losses	(116)	(165)
Total Fair Value	27,046	24,970
Total Gross Unrealized Losses	(535)	(321)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,060	3,096
Less than 12 Months, Gross Unrealized Losses	(49)	(9)
12 Months or Longer, Fair Value	0	1
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	1,060	3,097
Total Gross Unrealized Losses	(49)	(9)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	17,027	12,380
Less than 12 Months, Gross Unrealized Losses	(331)	(120)
12 Months or Longer, Fair Value	5,010	4,575
12 Months or Longer, Gross Unrealized Losses	(90)	(114)
Total Fair Value	22,037	16,955
Total Gross Unrealized Losses	(421)	(234)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	16,899	12,025
Less than 12 Months, Gross Unrealized Losses	(329)	(110)
12 Months or Longer, Fair Value	4,865	4,420
12 Months or Longer, Gross Unrealized Losses	(83)	(102)
Total Fair Value	21,764	16,445
Total Gross Unrealized Losses	(412)	(212)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	128	355
Less than 12 Months, Gross Unrealized Losses	(2)	(10)
12 Months or Longer, Fair Value	145	155
12 Months or Longer, Gross Unrealized Losses	(7)	(12)
Total Fair Value	273	510
Total Gross Unrealized Losses	(9)	(22)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,450	2,091
Less than 12 Months, Gross Unrealized Losses	(32)	(22)
12 Months or Longer, Fair Value	874	1,478
12 Months or Longer, Gross Unrealized Losses	(26)	(49)
Total Fair Value	3,324	3,569
Total Gross Unrealized Losses	(58)	(71)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,624	1,352
Less than 12 Months, Gross Unrealized Losses	(21)	(9)
12 Months or Longer, Fair Value	745	1,148
12 Months or Longer, Gross Unrealized Losses	(24)	(38)
Total Fair Value	2,369	2,500
Total Gross Unrealized Losses	(45)	(47)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	826	739
Less than 12 Months, Gross Unrealized Losses	(11)	(13)
12 Months or Longer, Fair Value	129	330
12 Months or Longer, Gross Unrealized Losses	(2)	(11)
Total Fair Value	955	1,069
Total Gross Unrealized Losses	(13)	(24)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	187	825
Less than 12 Months, Gross Unrealized Losses	(1)	(5)
12 Months or Longer, Fair Value	21	255
12 Months or Longer, Gross Unrealized Losses	0	(1)
Total Fair Value	208	1,080
Total Gross Unrealized Losses	(1)	(6)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	417	250
Less than 12 Months, Gross Unrealized Losses	(6)	0
12 Months or Longer, Fair Value	0	19
12 Months or Longer, Gross Unrealized Losses	0	(1)
Total Fair Value	417	269
Total Gross Unrealized Losses	$ (6)	$ (1)