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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 100,336 | $ 97,569
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 2,005 | 2,997
Gross Unrealized Losses | (574) | (120)
Fair Value | 101,766 | 100,445
Accrued interest receivable | 221 | 230
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,211 | 9,302
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 20 | 16
Gross Unrealized Losses | 0 | 0
Fair Value | 9,231 | 9,318
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 76,318 | 73,248
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 1,433 | 2,326
Gross Unrealized Losses | (545) | (108)
Fair Value | 77,206 | 75,466
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 908 | 1,035
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 209 | 204
Gross Unrealized Losses | 0 | (1)
Fair Value | 1,116 | 1,237
RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 77,226 | 74,283
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 1,642 | 2,530
Gross Unrealized Losses | (545) | (109)
Fair Value | 78,322 | 76,703
CMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 10,781 | 11,298
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 335 | 448
Gross Unrealized Losses | (29) | (11)
Fair Value | 11,087 | 11,735
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 3,118 | 2,686
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 8 | 3
Gross Unrealized Losses | 0 | 0
Fair Value | 3,126 | 2,689
Asset-backed Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value | $ 2,300 | $ 1,800

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