Derivatives - TBA Agency Securities (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Amount	$ 7,210,000,000	$ 5,337,000,000
TBA Agency Securities, 15-year, 1.5%
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.50%	1.50%
Notional Amount	$ 1,000,000,000	$ 200,000,000
Cost Basis	999,840,000	204,758,000
Fair Value	$ 1,003,125,000	$ 205,781,000
TBA Agency Securities, 15-year, 2.0%
Derivative [Line Items]
Derivative, Fixed Interest Rate	2.00%	2.00%
Notional Amount	$ 1,700,000,000	$ 1,200,000,000
Cost Basis	1,733,652,000	1,248,015,000
Fair Value	$ 1,738,695,000	$ 1,253,354,000
TBA Agency Securities, 30-year, 2.0%
Derivative [Line Items]
Derivative, Fixed Interest Rate	2.00%	2.00%
Notional Amount	$ 300,000,000	$ 600,000,000
Cost Basis	300,789,000	619,031,000
Fair Value	$ 299,227,000	$ 622,934,000
TBA Agency Securities, 30-year, 2.5%
Derivative [Line Items]
Derivative, Fixed Interest Rate	2.50%	2.50%
Notional Amount	$ 1,200,000,000	$ 800,000,000
Cost Basis	1,224,820,000	838,047,000
Fair Value	$ 1,223,510,000	841,314,000
TBA Agency Securities, 30-year, 3.0%
Derivative [Line Items]
Derivative, Fixed Interest Rate	3.00%
Notional Amount	$ 300,000,000
Cost Basis	309,734,000
Fair Value	$ 310,503,000
TBA Agency Securities, 30-year, 3.5%
Derivative [Line Items]
Derivative, Fixed Interest Rate	3.50%
Notional Amount		200,000,000
Cost Basis		(211,055,000)
Fair Value		(211,406,000)
TBA Agency Securities
Derivative [Line Items]
Notional Amount	$ 4,500,000,000	2,600,000,000
Cost Basis	4,568,835,000	2,698,796,000
Fair Value	4,575,060,000	2,711,977,000
Notional amount, forward settling	$ 400,000,000	$ 1,250,000,000