EQUITY (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended					12 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2023	Feb. 28, 2023
Class of Stock [Line Items]
Quarterly dividend on all classes of common stock (in dollars per share)		$ 1.40	$ 1.10	$ 1.10	$ 1.10	$ 1.10
Capital required for capital adequacy	$ 872.3	$ 872.3	$ 862.6				$ 862.6
Capital	1,500.0	1,500.0	1,500.0				1,500.0
Excess capital	$ 612.1	$ 612.1	$ 589.4				$ 589.4
Class C non-voting common stock
Class of Stock [Line Items]
Remaining authorized amount for repurchase								$ 9.8
Shares repurchased (in shares)	673,000						0
Shares repurchased	$ 19.8