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Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions | Sep. 30, 2024 USD ($) security | Dec. 31, 2023 USD ($) security
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Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | $ 6,551 | $ 5,068
Gross Unrealized Loss - Less than 12 Months | (15) | (50)
Fair Value - 12 Months or Longer | 59,724 | 62,711
Gross Unrealized Loss - 12 Months or Longer | (7,593) | (9,102)
Fair Value - Total | 66,275 | 67,779
Gross Unrealized Loss - Total | $ (7,608) | $ (9,152)
Number of securities in gross unrealized loss positions | security | 2,500 | 2,740
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | $ 3,772 | $ 733
Gross Unrealized Loss - Less than 12 Months | (4) | 0
Fair Value - 12 Months or Longer | 1,331 | 2,242
Gross Unrealized Loss - 12 Months or Longer | (9) | (49)
Fair Value - Total | 5,103 | 2,975
Gross Unrealized Loss - Total | (13) | (49)
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 1,807 | 3,511
Gross Unrealized Loss - Less than 12 Months | (10) | (43)
Fair Value - 12 Months or Longer | 52,413 | 53,987
Gross Unrealized Loss - 12 Months or Longer | (7,120) | (8,407)
Fair Value - Total | 54,220 | 57,498
Gross Unrealized Loss - Total | (7,130) | (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 | 10 | 13
Gross Unrealized Loss - 12 Months or Longer | 0 | (1)
Fair Value - Total | 14 | 14
Gross Unrealized Loss - Total | 0 | (1)
Total RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 1,811 | 3,512
Gross Unrealized Loss - Less than 12 Months | (10) | (43)
Fair Value - 12 Months or Longer | 52,423 | 54,000
Gross Unrealized Loss - 12 Months or Longer | (7,120) | (8,408)
Fair Value - Total | 54,234 | 57,512
Gross Unrealized Loss - Total | (7,130) | (8,451)
Agency CMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 192 | 547
Gross Unrealized Loss - Less than 12 Months | (1) | (7)
Fair Value - 12 Months or Longer | 5,966 | 6,465
Gross Unrealized Loss - 12 Months or Longer | (464) | (645)
Fair Value - Total | 6,158 | 7,012
Gross Unrealized Loss - Total | (465) | (652)
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 776 | 276
Gross Unrealized Loss - Less than 12 Months | 0 | 0
Fair Value - 12 Months or Longer | 4 | 4
Gross Unrealized Loss - 12 Months or Longer | 0 | 0
Fair Value - Total | 780 | 280
Gross Unrealized Loss - Total | $ 0 | $ 0

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