Investment Securities - Securities in Gross Unrealized Loss Position (Detail) $ in Millions	Mar. 31, 2020 USD ($) Security	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 4,087	$ 15,882
Fair Value - 12 Months or Longer	6,199	12,252
Fair Value - Total	10,286	28,134
Gross Unrealized Loss - Less than 12 Months	(59)	(120)
Gross Unrealized Loss - 12 Months or Longer	(86)	(212)
Gross Unrealized Loss - Total	$ (145)	(332)
Number of securities in gross unrealized loss positions \| Security	590
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months		2,647
Fair Value - 12 Months or Longer		0
Fair Value - Total		2,647
Gross Unrealized Loss - Less than 12 Months		(4)
Gross Unrealized Loss - 12 Months or Longer		0
Gross Unrealized Loss - Total		(4)
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 1,970	10,494
Fair Value - 12 Months or Longer	5,214	10,567
Fair Value - Total	7,184	21,061
Gross Unrealized Loss - Less than 12 Months	(29)	(92)
Gross Unrealized Loss - 12 Months or Longer	(74)	(192)
Gross Unrealized Loss - Total	(103)	(284)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	211	35
Fair Value - 12 Months or Longer	0	16
Fair Value - Total	211	51
Gross Unrealized Loss - Less than 12 Months	(12)	(1)
Gross Unrealized Loss - 12 Months or Longer	0	(1)
Gross Unrealized Loss - Total	(12)	(2)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	2,181	10,529
Fair Value - 12 Months or Longer	5,214	10,583
Fair Value - Total	7,395	21,112
Gross Unrealized Loss - Less than 12 Months	(41)	(93)
Gross Unrealized Loss - 12 Months or Longer	(74)	(193)
Gross Unrealized Loss - Total	(115)	(286)
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	1,351	2,580
Fair Value - 12 Months or Longer	985	1,563
Fair Value - Total	2,336	4,143
Gross Unrealized Loss - Less than 12 Months	(14)	(23)
Gross Unrealized Loss - 12 Months or Longer	(12)	(19)
Gross Unrealized Loss - Total	(26)	(42)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	555	126
Fair Value - 12 Months or Longer	0	106
Fair Value - Total	555	232
Gross Unrealized Loss - Less than 12 Months	(4)	0
Gross Unrealized Loss - 12 Months or Longer	0	0
Gross Unrealized Loss - Total	$ (4)	$ 0

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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