SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - RECENTLY ISSUED ACCOUNTING STANDARDS (NARRATIVE) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2021	Jan. 01, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income (loss)	$ (2,093.1)	$ 1,947.1
Retained earnings	1,459.0	1,127.2		$ 517.9
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in pre-tax impact to the insurance margins	35.0	45.0
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in pre-tax impact to the insurance margins	$ 55.0	$ 65.0
Cumulative Effect, Period of Adoption, Adjustment | Minimum | Accounting Standards Update 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income (loss)			$ (2,080.0)
Retained earnings			(130.0)
Cumulative Effect, Period of Adoption, Adjustment | Maximum | Accounting Standards Update 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive income (loss)			$ 110.0