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Investment Securities - Securities in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 15,882	$ 12,743
Fair Value - 12 Months or Longer	12,252	21,422
Fair Value - Total	28,134	34,165
Gross Unrealized Loss - Less than 12 Months	(120)	(297)
Gross Unrealized Loss - 12 Months or Longer	(212)	(675)
Gross Unrealized Loss - Total	(332)	(972)
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	2,647	2,543
Fair Value - 12 Months or Longer	0	1,076
Fair Value - Total	2,647	3,619
Gross Unrealized Loss - Less than 12 Months	(4)	(3)
Gross Unrealized Loss - 12 Months or Longer	0	(14)
Gross Unrealized Loss - Total	(4)	(17)
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	10,494	7,863
Fair Value - 12 Months or Longer	10,567	18,118
Fair Value - Total	21,061	25,981
Gross Unrealized Loss - Less than 12 Months	(92)	(260)
Gross Unrealized Loss - 12 Months or Longer	(192)	(609)
Gross Unrealized Loss - Total	(284)	(869)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	35	89
Fair Value - 12 Months or Longer	16	10
Fair Value - Total	51	99
Gross Unrealized Loss - Less than 12 Months	(1)	(2)
Gross Unrealized Loss - 12 Months or Longer	(1)	0
Gross Unrealized Loss - Total	(2)	(2)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	10,529	7,952
Fair Value - 12 Months or Longer	10,583	18,128
Fair Value - Total	21,112	26,080
Gross Unrealized Loss - Less than 12 Months	(93)	(262)
Gross Unrealized Loss - 12 Months or Longer	(193)	(609)
Gross Unrealized Loss - Total	(286)	(871)
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	2,580	2,004
Fair Value - 12 Months or Longer	1,563	1,540
Fair Value - Total	4,143	3,544
Gross Unrealized Loss - Less than 12 Months	(23)	(31)
Gross Unrealized Loss - 12 Months or Longer	(19)	(47)
Gross Unrealized Loss - Total	(42)	(78)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	126	244
Fair Value - 12 Months or Longer	106	678
Fair Value - Total	232	922
Gross Unrealized Loss - Less than 12 Months	0	(1)
Gross Unrealized Loss - 12 Months or Longer	0	(5)
Gross Unrealized Loss - Total	$ 0	$ (6)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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