REAL ESTATE AND OTHER SECURITIES - Schedule of Purchases and Sales of Real Estate and Other Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Treasury
Purchases
Face	$ 4,800.0	$ 0.0
Purchase price	4,773.9	0.0
Sales
Face	0.0	0.0
Amortized cost	0.0	0.0
Sale price	0.0	0.0
Realized gain (loss)	0.0	0.0
Agency
Purchases
Face	1,287.0	2,162.4
Purchase price	1,255.9	2,154.4
Sales
Face	0.0	1,462.4
Amortized cost	0.0	1,442.8
Sale price	0.0	1,395.9
Realized gain (loss)	0.0	(46.9)
Non-Agency
Purchases
Face	904.0	25.2
Purchase price	66.8	2.4
Sales
Face	0.0	0.0
Amortized cost	0.0	0.0
Sale price	0.0	0.0
Realized gain (loss)	$ 0.0	$ 0.0