INVESTMENTS - TOTAL INVESTMENT GAINS (LOSSES) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Realized investment gains (losses):
Total realized investment losses	$ (8.6)	$ (21.3)	$ (16.4)	$ (25.1)
Change in allowance for credit losses and write-downs	(3.5)	(1.0)	(13.1)	(10.7)
Change in fair value of equity securities	(1.9)	4.6	(3.9)	2.1
Other changes in fair value	(0.7)	(0.7)	(4.0)	8.5
Other investment gains (losses)	(6.1)	2.9	(21.0)	(0.1)
Total investment losses	(14.7)	(18.4)	(37.4)	(25.2)
Increase (decrease) in equity securities, FV-NI, held at end of period	(0.4)	4.2	(4.2)	4.8
Change in estimated fair value of trading securities	(0.3)	0.8	(3.3)	6.6
Embedded Derivative Related to Fixed Maturity Securities
Realized investment gains (losses):
Decrease in fair value of certain fixed maturity investments with embedded derivatives	(0.5)	(0.8)	(3.4)	7.2
Reinsurance Contract \| Coinsurance
Realized investment gains (losses):
Decrease in fair value of certain fixed maturity investments with embedded derivatives	(0.2)	0.1	(0.6)	1.3
Total fixed maturities, available for sale
Realized investment gains (losses):
Gross realized gains on sales of fixed maturities, available for sale	22.5	1.9	74.7	2.9
Gross realized losses on sales of fixed maturities, available for sale	(32.9)	(21.8)	(89.2)	(24.6)
Equity securities, net	1.6	(0.5)	(0.2)	(0.5)
Other, net	$ 0.2	$ (0.9)	$ (1.7)	$ (2.9)

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