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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 96,989 | $ 97,569
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 1,819 | 2,997
Gross Unrealized Losses | (658) | (120)
Fair Value | 98,149 | 100,445
Accrued interest receivable | 227 | 230
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,094 | 9,302
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 15 | 16
Gross Unrealized Losses | 0 | 0
Fair Value | 9,109 | 9,318
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 73,924 | 73,248
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 1,325 | 2,326
Gross Unrealized Losses | (617) | (108)
Fair Value | 74,632 | 75,466
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 844 | 1,035
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 206 | 204
Gross Unrealized Losses | 0 | (1)
Fair Value | 1,049 | 1,237
RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 74,768 | 74,283
Allowance for Credit Losses | (1) | (1)
Gross Unrealized Gains | 1,531 | 2,530
Gross Unrealized Losses | (617) | (109)
Fair Value | 75,681 | 76,703
CMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,973 | 11,298
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 265 | 448
Gross Unrealized Losses | (41) | (11)
Fair Value | 10,197 | 11,735
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 3,154 | 2,686
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 8 | 3
Gross Unrealized Losses | 0 | 0
Fair Value | 3,162 | 2,689
Asset-backed Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value | $ 2,300 | $ 1,800

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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