OTHER OPERATING STATEMENT DATA - SCHEDULE OF INSURANCE POLICY INCOME (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Direct premiums collected	$ 4,619.7	$ 4,457.7	$ 4,176.0
Reinsurance assumed	18.6	20.7	23.0
Reinsurance ceded	(214.6)	(231.3)	(247.8)
Premiums collected, net of reinsurance	4,423.7	4,247.1	3,951.2
Change in unearned premiums	9.8	0.9	9.2
Less premiums on interest-sensitive life and products without mortality and morbidity risk which are recorded as additions to insurance liabilities	(2,123.6)	(1,905.2)	(1,620.1)
Premiums on traditional products with mortality or morbidity risk	2,309.9	2,342.8	2,340.3
Fees and surrender charges on interest-sensitive products	189.9	180.6	171.0
Insurance policy income	2,499.8	2,523.4	$ 2,511.3
FABN Program
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Direct premiums collected	$ 899.0	$ 499.9