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Derivatives Volume of Activity (Details) | 6 Months Ended
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Jun. 30, 2020 USD ($)
Derivative [Line Items] |  |
Derivative Liability, Notional Amount | $ 1,225,000,000 | [1]
Not Designated as Hedging Instrument, Economic Hedge | Interest rate swaps |  |
Derivative [Line Items] |  |
Derivative Asset, Notional Amount | 4,225,000,000 |
Notional Amount of Derivative Instruments Added | 2,915,000,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (6,665,000,000) |
Derivative Asset, Notional Amount | 475,000,000 |
Not Designated as Hedging Instrument, Economic Hedge | Interest rate swaption |  |
Derivative [Line Items] |  |
Derivative Asset, Notional Amount | 750,000,000 | [2]
Notional Amount of Derivative Instruments Added | 0 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (750,000,000) |
Derivative Asset, Notional Amount | 0 |
Not Designated as Hedging Instrument, Economic Hedge | U.S. Treasury futures |  |
Derivative [Line Items] |  |
Derivative Liability, Notional Amount | 0 |
Notional Amount of Derivative Instruments Added | 2,212,600,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (3,437,600,000) |
Derivative Liability, Notional Amount | 1,225,000,000 |
Not Designated as Hedging Instrument, Economic Hedge | Options on U.S. Treasury futures |  |
Derivative [Line Items] |  |
Derivative Asset, Notional Amount | 1,350,000,000 | [2]
Notional Amount of Derivative Instruments Added | 3,425,000,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (3,350,000,000) |
Derivative Asset, Notional Amount | 1,425,000,000 | [1]
Not Designated as Hedging Instrument, Economic Hedge | TBA securities | Short position |  |
Derivative [Line Items] |  |
Derivative Liability, Notional Amount | 500,000,000 |
Notional Amount of Derivative Instruments Added | 3,017,000,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (3,517,000,000) |
Derivative Liability, Notional Amount | 0 |
Not Designated as Hedging Instrument, Trading | TBA securities | Long position |  |
Derivative [Line Items] |  |
Derivative Asset, Notional Amount | 435,000,000 |
Notional Amount of Derivative Instruments Added | 5,311,000,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (4,496,000,000) |
Derivative Asset, Notional Amount | $ 1,250,000,000 |
[1] | All futures and options outstanding as of June 30, 2020 will expire in September of 2020
[2] | All options outstanding as of December 31, 2019 expired during the first quarter of 2020.

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