Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 10,980	$ 30,629
Fair Value - 12 Months or Longer	60,388	40,544
Fair Value - Total	71,368	71,173
Gross Unrealized Loss - Less than 12 Months	(294)	(2,141)
Gross Unrealized Loss - 12 Months or Longer	(12,610)	(8,133)
Gross Unrealized Loss - Total	$ (12,904)	$ (10,274)
Number of securities in gross unrealized loss positions | security	2,910	2,840
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 2,410	$ 2,464
Fair Value - 12 Months or Longer	2,206	448
Fair Value - Total	4,616	2,912
Gross Unrealized Loss - Less than 12 Months	(1)	(57)
Gross Unrealized Loss - 12 Months or Longer	(74)	(33)
Gross Unrealized Loss - Total	(75)	(90)
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	6,472	23,271
Fair Value - 12 Months or Longer	51,771	36,803
Fair Value - Total	58,243	60,074
Gross Unrealized Loss - Less than 12 Months	(265)	(1,809)
Gross Unrealized Loss - 12 Months or Longer	(11,680)	(7,604)
Gross Unrealized Loss - Total	(11,945)	(9,413)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	5	14
Fair Value - 12 Months or Longer	11	3
Fair Value - Total	16	17
Gross Unrealized Loss - Less than 12 Months	0	(1)
Gross Unrealized Loss - 12 Months or Longer	(1)	0
Gross Unrealized Loss - Total	(1)	(1)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	6,477	23,285
Fair Value - 12 Months or Longer	51,782	36,806
Fair Value - Total	58,259	60,091
Gross Unrealized Loss - Less than 12 Months	(265)	(1,810)
Gross Unrealized Loss - 12 Months or Longer	(11,681)	(7,604)
Gross Unrealized Loss - Total	(11,946)	(9,414)
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	1,322	4,325
Fair Value - 12 Months or Longer	6,092	3,214
Fair Value - Total	7,414	7,539
Gross Unrealized Loss - Less than 12 Months	(26)	(267)
Gross Unrealized Loss - 12 Months or Longer	(854)	(493)
Gross Unrealized Loss - Total	(880)	(760)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	771	555
Fair Value - 12 Months or Longer	308	76
Fair Value - Total	1,079	631
Gross Unrealized Loss - Less than 12 Months	(2)	(7)
Gross Unrealized Loss - 12 Months or Longer	(1)	(3)
Gross Unrealized Loss - Total	$ (3)	$ (10)