Investment Securities - Schedule of Available-for-Sale Securities in Gross Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 7,339	$ 18,837
Less than 12 Months, Gross Unrealized Losses	(41)	(522)
12 Months or Longer, Fair Value	9,352	2,760
12 Months or Longer, Gross Unrealized Losses	(271)	(109)
Total Fair Value	16,691	21,597
Total Gross Unrealized Losses	(312)	(631)
U.S. Treasury debt obligations
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,340
Less than 12 Months, Gross Unrealized Losses	(2)
12 Months or Longer, Fair Value	0
12 Months or Longer, Gross Unrealized Losses	0
Total Fair Value	2,340
Total Gross Unrealized Losses	(2)
Corporate debt securities guaranteed by U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	187	1,143
Less than 12 Months, Gross Unrealized Losses	(3)	(47)
12 Months or Longer, Fair Value	554	46
12 Months or Longer, Gross Unrealized Losses	(20)	(2)
Total Fair Value	741	1,189
Total Gross Unrealized Losses	(23)	(49)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3,434	10,223
Less than 12 Months, Gross Unrealized Losses	(25)	(273)
12 Months or Longer, Fair Value	4,891	1,826
12 Months or Longer, Gross Unrealized Losses	(129)	(74)
Total Fair Value	8,325	12,049
Total Gross Unrealized Losses	(154)	(347)
RMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3,071	9,769
Less than 12 Months, Gross Unrealized Losses	(17)	(263)
12 Months or Longer, Fair Value	4,787	1,770
12 Months or Longer, Gross Unrealized Losses	(124)	(69)
Total Fair Value	7,858	11,539
Total Gross Unrealized Losses	(141)	(332)
RMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	363	454
Less than 12 Months, Gross Unrealized Losses	(8)	(10)
12 Months or Longer, Fair Value	104	56
12 Months or Longer, Gross Unrealized Losses	(5)	(5)
Total Fair Value	467	510
Total Gross Unrealized Losses	(13)	(15)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	952	3,794
Less than 12 Months, Gross Unrealized Losses	(10)	(117)
12 Months or Longer, Fair Value	2,616	439
12 Months or Longer, Gross Unrealized Losses	(89)	(27)
Total Fair Value	3,568	4,233
Total Gross Unrealized Losses	(99)	(144)
CMBS | Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	688	2,842
Less than 12 Months, Gross Unrealized Losses	(9)	(74)
12 Months or Longer, Fair Value	1,867	256
12 Months or Longer, Gross Unrealized Losses	(62)	(10)
Total Fair Value	2,555	3,098
Total Gross Unrealized Losses	(71)	(84)
CMBS | Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	264	952
Less than 12 Months, Gross Unrealized Losses	(1)	(43)
12 Months or Longer, Fair Value	749	183
12 Months or Longer, Gross Unrealized Losses	(27)	(17)
Total Fair Value	1,013	1,135
Total Gross Unrealized Losses	(28)	(60)
Other ABS
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	282	2,528
Less than 12 Months, Gross Unrealized Losses	0	(34)
12 Months or Longer, Fair Value	732	392
12 Months or Longer, Gross Unrealized Losses	(13)	(2)
Total Fair Value	1,014	2,920
Total Gross Unrealized Losses	(13)	(36)
Other securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	144	1,149
Less than 12 Months, Gross Unrealized Losses	(1)	(51)
12 Months or Longer, Fair Value	559	57
12 Months or Longer, Gross Unrealized Losses	(20)	(4)
Total Fair Value	703	1,206
Total Gross Unrealized Losses	$ (21)	$ (55)