INVESTMENTS - SUMMARY OF CARRYING VALUE AND ESTIMATED FAIR VALUE OF OUTSTANDING COMMERCIAL MORTGAGE LOANS AND UNDERLYING COLLATERAL (Details) $ in Millions	Sep. 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%
90% or greater \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	90.00%
Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2024	$ 125.8
2023	306.2
2022	308.9
2021	140.3
2020	37.9
Prior	599.5
Total amortized cost	1,518.6
Commercial mortgage loans	1,398.1
Collateral	4,744.3
Commercial Portfolio Segment \| Less than 60%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	109.5
2023	170.8
2022	130.8
2021	122.3
2020	37.9
Prior	490.2
Total amortized cost	1,061.5
Commercial mortgage loans	985.7
Collateral	4,106.3
Commercial Portfolio Segment \| 60% to less than 70%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	16.3
2023	93.0
2022	39.3
2021	12.2
2020	0.0
Prior	28.8
Total amortized cost	189.6
Commercial mortgage loans	178.4
Collateral	292.4
Commercial Portfolio Segment \| 70% to less than 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	0.0
2023	42.4
2022	69.7
2021	5.8
2020	0.0
Prior	48.6
Total amortized cost	166.5
Commercial mortgage loans	149.4
Collateral	224.5
Commercial Portfolio Segment \| 80% to less than 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2024	0.0
2023	0.0
2022	69.1
2021	0.0
2020	0.0
Prior	17.2
Total amortized cost	86.3
Commercial mortgage loans	74.2
Collateral	106.0
Commercial Portfolio Segment \| 90% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
2024	0.0
2023	0.0
2022	0.0
2021	0.0
2020	0.0
Prior	14.7
Total amortized cost	14.7
Commercial mortgage loans	10.4
Collateral	$ 15.1

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