Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions	Jun. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 7,702	$ 5,068
Gross Unrealized Loss - Less than 12 Months	(52)	(50)
Fair Value - 12 Months or Longer	61,421	62,711
Gross Unrealized Loss - 12 Months or Longer	(10,406)	(9,102)
Fair Value - Total	69,123	67,779
Gross Unrealized Loss - Total	$ (10,458)	$ (9,152)
Number of securities in gross unrealized loss positions | security	2,790	2,740
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 1,329	$ 733
Gross Unrealized Loss - Less than 12 Months	(3)	0
Fair Value - 12 Months or Longer	2,014	2,242
Gross Unrealized Loss - 12 Months or Longer	(23)	(49)
Fair Value - Total	3,343	2,975
Gross Unrealized Loss - Total	(26)	(49)
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	5,024	3,511
Gross Unrealized Loss - Less than 12 Months	(42)	(43)
Fair Value - 12 Months or Longer	53,037	53,987
Gross Unrealized Loss - 12 Months or Longer	(9,714)	(8,407)
Fair Value - Total	58,061	57,498
Gross Unrealized Loss - Total	(9,756)	(8,450)
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	4	1
Gross Unrealized Loss - Less than 12 Months	0	0
Fair Value - 12 Months or Longer	12	13
Gross Unrealized Loss - 12 Months or Longer	(1)	(1)
Fair Value - Total	16	14
Gross Unrealized Loss - Total	(1)	(1)
Total RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	5,028	3,512
Gross Unrealized Loss - Less than 12 Months	(42)	(43)
Fair Value - 12 Months or Longer	53,049	54,000
Gross Unrealized Loss - 12 Months or Longer	(9,715)	(8,408)
Fair Value - Total	58,077	57,512
Gross Unrealized Loss - Total	(9,757)	(8,451)
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	632	547
Gross Unrealized Loss - Less than 12 Months	(7)	(7)
Fair Value - 12 Months or Longer	6,262	6,465
Gross Unrealized Loss - 12 Months or Longer	(668)	(645)
Fair Value - Total	6,894	7,012
Gross Unrealized Loss - Total	(675)	(652)
Other securities
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	713	276
Gross Unrealized Loss - Less than 12 Months	0	0
Fair Value - 12 Months or Longer	96	4
Gross Unrealized Loss - 12 Months or Longer	0	0
Fair Value - Total	809	280
Gross Unrealized Loss - Total	$ 0	$ 0