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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 88,459 | $ 88,063
Allowance for Credit Losses | (4) | (4)
Gross Unrealized Gains | 186 | 214
Gross Unrealized Losses | (10,243) | (9,156)
Fair Value | 78,398 | 79,117
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 5,764 | 5,330
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 3 | 1
Gross Unrealized Losses | (39) | (49)
Fair Value | 5,728 | 5,282
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 71,153 | 71,294
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 74 | 104
Gross Unrealized Losses | (9,506) | (8,450)
Fair Value | 61,721 | 62,948
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 600 | 610
Allowance for Credit Losses | (4) | (4)
Gross Unrealized Gains | 86 | 89
Gross Unrealized Losses | (5) | (5)
Fair Value | 677 | 690
Total RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 71,753 | 71,904
Allowance for Credit Losses | (4) | (4)
Gross Unrealized Gains | 160 | 193
Gross Unrealized Losses | (9,511) | (8,455)
Fair Value | 62,398 | 63,638
Agency CMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 8,867 | 8,961
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 19 | 14
Gross Unrealized Losses | (693) | (652)
Fair Value | 8,193 | 8,323
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 2,075 | 1,868
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 4 | 6
Gross Unrealized Losses | 0 | 0
Fair Value | 2,079 | 1,874
Asset-backed Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value | $ 1,600 | $ 1,400

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 + Details
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