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Investment Securities - Securities in Gross Unrealized Loss Position (Details) $ in Millions | Mar. 31, 2021 USD ($) security | Dec. 31, 2020 USD ($) security
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | $ 35,491 | $ 9,095
Fair Value - 12 Months or Longer | 1,714 | 2,059
Fair Value - Total | 37,205 | 11,154
Gross Unrealized Loss - Less than 12 Months | (789) | (64)
Gross Unrealized Loss - 12 Months or Longer | (50) | (55)
Gross Unrealized Loss - Total | $ (839) | $ (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 | $ 33,027 | $ 7,424
Fair Value - 12 Months or Longer | 1,558 | 1,791
Fair Value - Total | 34,585 | 9,215
Gross Unrealized Loss - Less than 12 Months | (733) | (57)
Gross Unrealized Loss - 12 Months or Longer | (50) | (51)
Gross Unrealized Loss - Total | (783) | (108)
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 10 | 12
Fair Value - 12 Months or Longer | 1 | 0
Fair Value - Total | 11 | 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 | 33,037 | 7,436
Fair Value - 12 Months or Longer | 1,559 | 1,791
Fair Value - Total | 34,596 | 9,227
Gross Unrealized Loss - Less than 12 Months | (733) | (57)
Gross Unrealized Loss - 12 Months or Longer | (50) | (51)
Gross Unrealized Loss - Total | (783) | (108)
CMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 2,083 | 1,545
Fair Value - 12 Months or Longer | 155 | 267
Fair Value - Total | 2,238 | 1,812
Gross Unrealized Loss - Less than 12 Months | (56) | (7)
Gross Unrealized Loss - 12 Months or Longer | 0 | (4)
Gross Unrealized Loss - Total | (56) | (11)
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value - Less than 12 Months | 371 | 114
Fair Value - 12 Months or Longer | 0 | 1
Fair Value - Total | 371 | 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

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- Definition Amount of accumulated unrealized loss on 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 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922890-210455 + Details
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