INVESTMENTS - NET REALIZED INVESTMENT GAINS (LOSSES) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Gain (Loss) on Securities [Line Items]
Total realized gains (losses)	$ 31.3	$ 43.8	$ 28.5	$ (71.7)
Change in allowance for credit losses and other-than-temporary impairment losses of other investments	2.7	6.7	15.4	(22.8)
Increase (decrease) in estimated fair value of equity securities			0.4	(7.6)
Variable interest entities, change in allowance for current expected credit losses	2.2	9.9	11.9	(17.9)
Change in estimated fair value of trading securities			0.7	(6.6)
Total fixed maturities, available for sale
Gain (Loss) on Securities [Line Items]
Gross realized gains on sale	25.5	26.9	38.7	38.8
Gross realized losses on sale	(4.4)	(29.0)	(18.2)	(50.4)
Change in allowance for credit losses and other-than-temporary impairment losses	3.0	9.2	(0.1)	(16.7)
Total realized gains (losses)	24.1	7.1	20.4	(28.3)
Equity securities - corporate securities
Gain (Loss) on Securities [Line Items]
Total realized gains (losses)	1.6	5.5	(0.2)	(10.2)
Other
Gain (Loss) on Securities [Line Items]
Total realized gains (losses)	$ 2.9	$ 24.5	$ (7.1)	$ (10.4)

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