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Investment Securities - Available-for-Sale Securities (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 77,984 | $ 46,728
Gross Unrealized Gains | 1,561 | 394
Gross Unrealized Losses | (332) | (972)
Fair Value | 79,213 | 46,150
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 4,122 | 6,146
Gross Unrealized Gains | 6 | 15
Gross Unrealized Losses | (4) | (17)
Fair Value | 4,124 | 6,144
RMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 62,003 | 32,710
Gross Unrealized Gains | 1,120 | 62
Gross Unrealized Losses | (284) | (869)
Fair Value | 62,839 | 31,903
RMBS, Non-agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,235 | 1,440
Gross Unrealized Gains | 266 | 304
Gross Unrealized Losses | (2) | (2)
Fair Value | 1,499 | 1,742
RMBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 63,238 | 34,150
Gross Unrealized Gains | 1,386 | 366
Gross Unrealized Losses | (286) | (871)
Fair Value | 64,338 | 33,645
CMBS, Agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,303 | 4,806
Gross Unrealized Gains | 165 | 11
Gross Unrealized Losses | (42) | (78)
Fair Value | 9,426 | 4,739
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,321 | 1,626
Gross Unrealized Gains | 4 | 2
Gross Unrealized Losses | 0 | (6)
Fair Value | $ 1,325 | $ 1,622

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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=118939692&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss 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 (c) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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