Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 17,401	$ 21,141
Less than 12 Months, Gross Unrealized Losses	(253)	(419)
12 Months or Longer, Fair Value	5,805	5,905
12 Months or Longer, Gross Unrealized Losses	(107)	(116)
Total Fair Value	23,206	27,046
Total Gross Unrealized Losses	(360)	(535)
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,079	1,060
Less than 12 Months, Gross Unrealized Losses	(30)	(49)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	1,079	1,060
Total Gross Unrealized Losses	(30)	(49)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	14,503	17,027
Less than 12 Months, Gross Unrealized Losses	(211)	(331)
12 Months or Longer, Fair Value	4,894	5,010
12 Months or Longer, Gross Unrealized Losses	(85)	(90)
Total Fair Value	19,397	22,037
Total Gross Unrealized Losses	(296)	(421)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	14,491	16,899
Less than 12 Months, Gross Unrealized Losses	(211)	(329)
12 Months or Longer, Fair Value	4,845	4,865
12 Months or Longer, Gross Unrealized Losses	(81)	(83)
Total Fair Value	19,336	21,764
Total Gross Unrealized Losses	(292)	(412)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	12	128
Less than 12 Months, Gross Unrealized Losses	0	(2)
12 Months or Longer, Fair Value	49	145
12 Months or Longer, Gross Unrealized Losses	(4)	(7)
Total Fair Value	61	273
Total Gross Unrealized Losses	(4)	(9)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,351	2,450
Less than 12 Months, Gross Unrealized Losses	(12)	(32)
12 Months or Longer, Fair Value	894	874
12 Months or Longer, Gross Unrealized Losses	(22)	(26)
Total Fair Value	2,245	3,324
Total Gross Unrealized Losses	(34)	(58)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	977	1,624
Less than 12 Months, Gross Unrealized Losses	(9)	(21)
12 Months or Longer, Fair Value	833	745
12 Months or Longer, Gross Unrealized Losses	(22)	(24)
Total Fair Value	1,810	2,369
Total Gross Unrealized Losses	(31)	(45)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	374	826
Less than 12 Months, Gross Unrealized Losses	(3)	(11)
12 Months or Longer, Fair Value	61	129
12 Months or Longer, Gross Unrealized Losses	0	(2)
Total Fair Value	435	955
Total Gross Unrealized Losses	(3)	(13)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	113	187
Less than 12 Months, Gross Unrealized Losses	0	(1)
12 Months or Longer, Fair Value	17	21
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	130	208
Total Gross Unrealized Losses	0	(1)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	355	417
Less than 12 Months, Gross Unrealized Losses	0	(6)
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Gross Unrealized Losses	0	0
Total Fair Value	355	417
Total Gross Unrealized Losses	$ 0	$ (6)