FAIR VALUE OF ASSETS AND LIABILITIES - Fair Value of Financial Instruments Held by Consolidated Investments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign time deposits	$ 0.0	$ 25.7
Assets held for policyholders	393.9	668.7
Policyholder payables	(393.9)	(668.7)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,469.2	1,234.7
Equity investments	272.4	325.0
Foreign time deposits	0.0	25.7
Assets held for policyholders	393.9	668.7
Policyholder payables	(393.9)	(668.7)
Fair Value | Total Return Swap
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total return swap related to deferred compensation plans	$ 4.9	$ (1.6)