Derivatives - TBA Agency Securities (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Notional Amount	$ 7,410,000,000	$ 7,210,000,000
Notional amount, forward settling	$ 950,000,000
TBA Agency Securities, 15-year, 1.5%
Derivative [Line Items]
Fixed interest rate		1.50%
Notional Amount		$ 1,000,000,000
Cost Basis		999,840,000
Fair Value		$ 1,003,125,000
TBA Agency Securities, 15-year, 2.0%
Derivative [Line Items]
Fixed interest rate		2.00%
Notional Amount		$ 1,700,000,000
Cost Basis		1,733,652,000
Fair Value		$ 1,738,695,000
TBA Agency Securities, 30-year, 2.0%
Derivative [Line Items]
Fixed interest rate		2.00%
Notional Amount		$ 300,000,000
Cost Basis		300,789,000
Fair Value		$ 299,227,000
TBA Agency Securities, 30-year, 2.5%
Derivative [Line Items]
Fixed interest rate		2.50%
Notional Amount		$ 1,200,000,000
Cost Basis		1,224,820,000
Fair Value		$ 1,223,510,000
TBA Agency Securities, 30-year, 3.0%
Derivative [Line Items]
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, 4.0%
Derivative [Line Items]
Fixed interest rate	4.00%
Notional Amount	$ 750,000,000
Cost Basis	760,449,000
Fair Value	763,273,000
TBA Agency Securities
Derivative [Line Items]
Notional Amount	750,000,000	4,500,000,000
Cost Basis	760,449,000	4,568,835,000
Fair Value	763,273,000	4,575,060,000
Notional amount, forward settling	$ 200,000,000	$ 400,000,000