REAL ESTATE AND OTHER SECURITIES - Schedule of Investment in Real Estate Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Treasury
Purchases
Face	$ 1,055.0	$ 0.0
Purchase price	1,028.1	0.0
Sales
Face	0.0	0.0
Amortized cost	0.0	0.0
Sale price	0.0	0.0
Gain (loss) on sale	0.0	0.0
Agency
Purchases
Face	3,373.7	16,479.3
Purchase price	3,350.6	16,314.6
Sales
Face	1,691.5	16,516.0
Amortized cost	1,671.7	16,759.7
Sale price	1,614.7	15,026.3
Gain (loss) on sale	(57.0)	(1,733.4)
Non-Agency
Purchases
Face	2,816.9	5,018.1
Purchase price	347.2	256.5
Sales
Face	0.0	15.3
Amortized cost	0.2	13.6
Sale price	0.0	12.0
Gain (loss) on sale	$ (0.2)	$ (1.6)