INVESTMENTS - SUMMARY OF CARRYING VALUE AND ESTIMATED FAIR VALUE OF OUTSTANDING COMMERCIAL MORTGAGE LOANS AND UNDERLYING COLLATERAL (Details) $ in Millions	Sep. 30, 2023 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%
Debt-To-Value Ratio, Greater Than 90 Percent \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	90.00%
Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2023	$ 230.2
2022	312.4
2021	151.0
2020	42.3
2019	73.8
Prior	600.9
Total amortized cost	1,410.6
Mortgage loans	1,217.8
Collateral	4,336.7
Commercial Portfolio Segment \| Less than 60%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	163.6
2022	147.3
2021	115.1
2020	36.7
2019	73.8
Prior	482.3
Total amortized cost	1,018.8
Mortgage loans	880.8
Collateral	3,789.7
Commercial Portfolio Segment \| 60% to less than 70%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	47.1
2022	87.3
2021	11.1
2020	5.6
2019	0.0
Prior	36.8
Total amortized cost	187.9
Mortgage loans	165.5
Collateral	287.0
Commercial Portfolio Segment \| 70% to less than 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	19.5
2022	77.8
2021	24.8
2020	0.0
2019	0.0
Prior	40.1
Total amortized cost	162.2
Mortgage loans	138.7
Collateral	214.1
Commercial Portfolio Segment \| 80% to less than 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0.0
2022	0.0
2021	0.0
2020	0.0
2019	0.0
Prior	17.4
Total amortized cost	17.4
Mortgage loans	15.8
Collateral	20.8
Commercial Portfolio Segment \| 90% or greater
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0.0
2022	0.0
2021	0.0
2020	0.0
2019	0.0
Prior	24.3
Total amortized cost	24.3
Mortgage loans	17.0
Collateral	$ 25.1

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Amortized cost of financing receivable originated more than five years prior to current fiscal year. Excludes net investment in lease.

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