INVESTMENTS - SUMMARY OF CARRYING VALUE AND ESTIMATED FAIR VALUE OF OUTSTANDING COMMERCIAL MORTGAGE LOANS AND UNDERLYING COLLATERAL (Details) $ in Millions	Jun. 30, 2024 USD ($)
Less than 60% \| Maximum
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%
60% to less than 70% \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	60.00%
70% to less than 80% \| Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	80.00%
70% to less than 80% \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	70.00%
80% to less than 90% \| Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	90.00%
80% to less than 90% \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	80.00%
Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2024	$ 81.3
2023	306.5
2022	309.8
2021	140.7
2020	38.3
Prior	610.6
Total amortized cost	1,487.2
Commercial mortgage loans	1,315.6
Collateral	4,572.0
Commercial Portfolio Segment \| Less than 60%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	65.0
2023	160.4
2022	159.9
2021	111.7
2020	32.9
Prior	511.9
Total amortized cost	1,041.8
Commercial mortgage loans	928.5
Collateral	3,934.4
Commercial Portfolio Segment \| 60% to less than 70%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	16.3
2023	126.9
2022	72.1
2021	29.0
2020	5.4
Prior	17.6
Total amortized cost	267.3
Commercial mortgage loans	245.1
Collateral	410.9
Commercial Portfolio Segment \| 70% to less than 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	0.0
2023	19.2
2022	30.0
2021	0.0
2020	0.0
Prior	35.2
Total amortized cost	84.4
Commercial mortgage loans	67.4
Collateral	114.9
Commercial Portfolio Segment \| 80% to less than 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	0.0
2023	0.0
2022	47.8
2021	0.0
2020	0.0
Prior	45.9
Total amortized cost	93.7
Commercial mortgage loans	74.6
Collateral	$ 111.8

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