Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions	Jun. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 36,728	$ 9,095
Fair Value - 12 Months or Longer	1,908	2,059
Fair Value - Total	38,636	11,154
Gross Unrealized Loss - Less than 12 Months	(512)	(64)
Gross Unrealized Loss - 12 Months or Longer	(61)	(55)
Gross Unrealized Loss - Total	$ (573)	$ (119)
Number of securities in gross unrealized loss positions \| security	570	320
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 34,165	$ 7,424
Fair Value - 12 Months or Longer	1,685	1,791
Fair Value - Total	35,850	9,215
Gross Unrealized Loss - Less than 12 Months	(485)	(57)
Gross Unrealized Loss - 12 Months or Longer	(59)	(51)
Gross Unrealized Loss - Total	(544)	(108)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	6	12
Fair Value - 12 Months or Longer	0	0
Fair Value - Total	6	12
Gross Unrealized Loss - Less than 12 Months	0	0
Gross Unrealized Loss - 12 Months or Longer	0	0
Gross Unrealized Loss - Total	0	0
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	34,171	7,436
Fair Value - 12 Months or Longer	1,685	1,791
Fair Value - Total	35,856	9,227
Gross Unrealized Loss - Less than 12 Months	(485)	(57)
Gross Unrealized Loss - 12 Months or Longer	(59)	(51)
Gross Unrealized Loss - Total	(544)	(108)
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	2,028	1,545
Fair Value - 12 Months or Longer	223	267
Fair Value - Total	2,251	1,812
Gross Unrealized Loss - Less than 12 Months	(27)	(7)
Gross Unrealized Loss - 12 Months or Longer	(2)	(4)
Gross Unrealized Loss - Total	(29)	(11)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	529	114
Fair Value - 12 Months or Longer	0	1
Fair Value - Total	529	115
Gross Unrealized Loss - Less than 12 Months	0	0
Gross Unrealized Loss - 12 Months or Longer	0	0
Gross Unrealized Loss - Total	$ 0	$ 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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