Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 20,825	$ 21,141
Less than 12 Months, Gross Unrealized Losses	(397)	(419)
12 Months or Longer, Fair Value	5,397	5,905
12 Months or Longer, Gross Unrealized Losses	(104)	(116)
Total Fair Value	26,222	27,046
Total Gross Unrealized Losses	(501)	(535)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,067	1,060
Less than 12 Months, Gross Unrealized Losses	(42)	(49)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	1,067	1,060
Total Gross Unrealized Losses	(42)	(49)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	17,105	17,027
Less than 12 Months, Gross Unrealized Losses	(324)	(331)
12 Months or Longer, Fair Value	4,572	5,010
12 Months or Longer, Gross Unrealized Losses	(81)	(90)
Total Fair Value	21,677	22,037
Total Gross Unrealized Losses	(405)	(421)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	17,055	16,899
Less than 12 Months, Gross Unrealized Losses	(323)	(329)
12 Months or Longer, Fair Value	4,458	4,865
12 Months or Longer, Gross Unrealized Losses	(76)	(83)
Total Fair Value	21,513	21,764
Total Gross Unrealized Losses	(399)	(412)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	50	128
Less than 12 Months, Gross Unrealized Losses	(1)	(2)
12 Months or Longer, Fair Value	114	145
12 Months or Longer, Gross Unrealized Losses	(5)	(7)
Total Fair Value	164	273
Total Gross Unrealized Losses	(6)	(9)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,966	2,450
Less than 12 Months, Gross Unrealized Losses	(26)	(32)
12 Months or Longer, Fair Value	805	874
12 Months or Longer, Gross Unrealized Losses	(22)	(26)
Total Fair Value	2,771	3,324
Total Gross Unrealized Losses	(48)	(58)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,354	1,624
Less than 12 Months, Gross Unrealized Losses	(20)	(21)
12 Months or Longer, Fair Value	715	745
12 Months or Longer, Gross Unrealized Losses	(22)	(24)
Total Fair Value	2,069	2,369
Total Gross Unrealized Losses	(42)	(45)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	612	826
Less than 12 Months, Gross Unrealized Losses	(6)	(11)
12 Months or Longer, Fair Value	90	129
12 Months or Longer, Gross Unrealized Losses	0	(2)
Total Fair Value	702	955
Total Gross Unrealized Losses	(6)	(13)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	199	187
Less than 12 Months, Gross Unrealized Losses	(1)	(1)
12 Months or Longer, Fair Value	19	21
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	218	208
Total Gross Unrealized Losses	(1)	(1)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	488	417
Less than 12 Months, Gross Unrealized Losses	(4)	(6)
12 Months or Longer, Fair Value	1	0
12 Months or Longer, Gross Unrealized Losses	(1)	0
Total Fair Value	489	417
Total Gross Unrealized Losses	$ (5)	$ (6)