REAL ESTATE AND OTHER SECURITIES - Schedule of Investment in Real Estate Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Treasury
Purchases
Face	$ 0.0		$ 1,000.0
Purchase price	0.0		973.8
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	1,211.3	$ 9,053.2	3,373.7	$ 10,051.4
Purchase price	1,196.2	9,041.6	3,350.6	10,046.1
Sales
Face	230.0	7,767.1	1,692.4	8,596.9
Amortized cost	229.8	7,987.1	1,672.6	8,844.1
Sale price	219.6	6,965.4	1,615.5	7,704.3
Gain (loss) on sale	(10.2)	(1,021.8)	(57.1)	(1,139.9)
Non-Agency
Purchases
Face	0.0	906.7	472.6	4,189.8
Purchase price	0.0	69.1	32.6	217.7
Sales
Face	0.0	15.3	0.0	15.3
Amortized cost	0.0	12.0	0.2	13.6
Sale price	0.0	12.0	0.0	12.0
Gain (loss) on sale	$ 0.0	$ (0.1)	$ (0.2)	$ (1.6)