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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 97,569 | $ 77,984
Allowance for Credit Losses | (1) |
Gross Unrealized Gains | 2,997 | 1,561
Gross Unrealized Losses | (120) | (332)
Fair Value | 100,445 | 79,213
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,302 | 4,122
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 16 | 6
Gross Unrealized Losses | 0 | (4)
Fair Value | 9,318 | 4,124
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 73,248 | 62,003
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 2,326 | 1,120
Gross Unrealized Losses | (108) | (284)
Fair Value | 75,466 | 62,839
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,035 | 1,235
Allowance for Credit Losses | (1) |
Gross Unrealized Gains | 204 | 266
Gross Unrealized Losses | (1) | (2)
Fair Value | 1,237 | 1,499
RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 74,283 | 63,238
Allowance for Credit Losses | (1) |
Gross Unrealized Gains | 2,530 | 1,386
Gross Unrealized Losses | (109) | (286)
Fair Value | 76,703 | 64,338
CMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 11,298 | 9,303
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 448 | 165
Gross Unrealized Losses | (11) | (42)
Fair Value | 11,735 | 9,426
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 2,686 | 1,321
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 3 | 4
Gross Unrealized Losses | 0 | 0
Fair Value | 2,689 | 1,325
Asset-backed Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fair Value | $ 1,800 | $ 117

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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=121645371&loc=d3e27161-111563 + Details
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