LIABILITIES FOR INSURANCE PRODUCTS - SUMMARY OF LIABILITIES FOR UNPAID CLAIMS ADJUSTMENT EXPENSE (Details) - Accident and Health Insurance Product Line - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance, beginning of year	$ 1,742.2	$ 1,825.0	$ 1,921.2
Less reinsurance (receivables) payables	(863.2)	(814.6)	(881.5)	$ (993.2)
Net balance, beginning of year	927.6	943.5	928.0
Incurred claims related to:
Current year	1,177.8	1,205.0	1,177.8
Prior years	(111.2)	(111.5)	(75.2)
Total incurred	1,066.6	1,093.5	1,102.6
Interest on claim reserves	33.1	34.8	36.8
Paid claims related to:
Current year	(789.6)	(802.9)	(766.1)
Prior years	(342.6)	(341.3)	(357.8)
Total paid	(1,132.2)	(1,144.2)	(1,123.9)
Net balance, end of year	895.1	927.6	943.5
Add reinsurance receivables (payables)	863.2	814.6	881.5	$ 993.2
Balance, end of year	$ 1,758.3	$ 1,742.2	$ 1,825.0