INVESTMENTS - SUMMARY OF WEIGHTED AVERAGE LOAN-TO-VALUE RATIO FOR OUTSTANDING MORTGAGE LOANS (Details) $ in Millions	Dec. 31, 2022 USD ($)
Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	$ 314.3
2021	150.5
2020	43.5
2019	75.4
2018	74.7
Prior	573.8
Total amortized cost	1,232.2
Mortgage loans	1,082.9
Collateral	4,333.3
Less than 60% | Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	234.1
2021	114.7
2020	43.5
2019	75.4
2018	66.5
Prior	476.3
Total amortized cost	1,010.5
Mortgage loans	889.8
Collateral	$ 4,027.6
Less than 60% | Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	60.00%
60% to less than 70% | Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	$ 47.2
2021	13.2
2020	0.0
2019	0.0
2018	8.2
Prior	45.0
Total amortized cost	113.6
Mortgage loans	104.7
Collateral	$ 170.7
60% to less than 70% | Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	60.00%
60% to less than 70% | Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	70.00%
70% to less than 80% | Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	$ 33.0
2021	22.6
2020	0.0
2019	0.0
2018	0.0
Prior	0.0
Total amortized cost	55.6
Mortgage loans	47.2
Collateral	$ 72.3
70% to less than 80% | Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	70.00%
70% to less than 80% | Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	80.00%
80% to less than 90% | Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	$ 0.0
2021	0.0
2020	0.0
2019	0.0
2018	0.0
Prior	42.5
Total amortized cost	42.5
Mortgage loans	34.5
Collateral	$ 52.0
80% to less than 90% | Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	80.00%
80% to less than 90% | Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	90.00%
90% or greater | Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2022	$ 0.0
2021	0.0
2020	0.0
2019	0.0
2018	0.0
Prior	10.0
Total amortized cost	10.0
Mortgage loans	6.7
Collateral	$ 10.7
90% or greater | Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan-to-value ratio	90.00%