Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 37,631	$ 9,095
Fair Value - 12 Months or Longer	4,630	2,059
Fair Value - Total	42,261	11,154
Gross Unrealized Loss - Less than 12 Months	(545)	(64)
Gross Unrealized Loss - 12 Months or Longer	(113)	(55)
Gross Unrealized Loss - Total	$ (658)	$ (119)
Number of securities in gross unrealized loss positions \| security	540	320
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 35,415	$ 7,424
Fair Value - 12 Months or Longer	4,068	1,791
Fair Value - Total	39,483	9,215
Gross Unrealized Loss - Less than 12 Months	(519)	(57)
Gross Unrealized Loss - 12 Months or Longer	(98)	(51)
Gross Unrealized Loss - Total	(617)	(108)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	0	12
Fair Value - 12 Months or Longer	1	0
Fair Value - Total	1	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	35,415	7,436
Fair Value - 12 Months or Longer	4,069	1,791
Fair Value - Total	39,484	9,227
Gross Unrealized Loss - Less than 12 Months	(519)	(57)
Gross Unrealized Loss - 12 Months or Longer	(98)	(51)
Gross Unrealized Loss - Total	(617)	(108)
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	1,746	1,545
Fair Value - 12 Months or Longer	561	267
Fair Value - Total	2,307	1,812
Gross Unrealized Loss - Less than 12 Months	(26)	(7)
Gross Unrealized Loss - 12 Months or Longer	(15)	(4)
Gross Unrealized Loss - Total	(41)	(11)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	470	114
Fair Value - 12 Months or Longer	0	1
Fair Value - Total	470	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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