FAIR VALUE OF ASSETS AND LIABILITIES - Fair Value of Financial Instruments Held by Consolidated Investments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,009.9	$ 1,234.7	$ 936.8
Foreign time deposits	15.1	25.7
Assets held for policyholders	444.0	668.7
Policyholder payables	(444.0)	(668.7)
Total return swaps related to deferred compensation plans	19.3
Total return swaps related to deferred compensation plans		(1.6)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,009.9	1,234.7
Equity investments	282.9	325.0
Foreign time deposits	15.1	25.7
Assets held for policyholders	444.0	668.7
Policyholder payables	(444.0)	(668.7)
Fair Value | Total return swaps related to deferred compensation plans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total return swaps related to deferred compensation plans	$ 19.3
Total return swaps related to deferred compensation plans		$ (1.6)