Derivatives Volume of Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Not Designated as Hedging Instrument, Economic Hedge | Interest rate swaptions
Derivative [Line Items]
Derivative, Notional Amount	$ (500,000)	$ (1,250,000)
Additions	(500,000)
Settlements, Terminations, or Pair-Offs	(1,250,000)
Not Designated as Hedging Instrument, Economic Hedge | U.S. Treasury futures | Short position
Derivative [Line Items]
Derivative, Notional Amount	(3,890,000)	(825,000)
Additions	(15,880,000)
Settlements, Terminations, or Pair-Offs	(12,815,000)
Not Designated as Hedging Instrument, Economic Hedge | Options on U.S. Treasury futures | Long position
Derivative [Line Items]
Derivative, Notional Amount	0	(500,000)
Additions	(2,350,000)
Settlements, Terminations, or Pair-Offs	(2,850,000)
Not Designated as Hedging Instrument, Trading | TBA securities | Long position
Derivative [Line Items]
Derivative, Notional Amount	(1,530,000)	$ (1,515,000)
Additions	(22,920,000)
Settlements, Terminations, or Pair-Offs	$ (22,905,000)