INVESTMENTS - SUMMARY OF CARRYING VALUE AND ESTIMATED FAIR VALUE OF OUTSTANDING COMMERCIAL MORTGAGE LOANS AND UNDERLYING COLLATERAL (Details) $ in Millions	Sep. 30, 2025 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% to less than 100% \| Maximum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	100.00%
90% to less than 100% \| Minimum
Financing Receivable, Credit Quality Indicator [Line Items]
Loan to value ratio	90.00%
Commercial Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2025	$ 280.7
2024	184.4
2023	275.5
2022	278.2
2021	139.0
Prior	516.2
Total amortized cost	1,674.0
Commercial mortgage loans	1,577.1
Collateral	4,629.0
Commercial Portfolio Segment \| Less than 60%
Financing Receivable, Credit Quality Indicator [Line Items]
2025	165.2
2024	169.4
2023	179.5
2022	142.1
2021	113.2
Prior	455.2
Total amortized cost	1,224.6
Commercial mortgage loans	1,165.6
Collateral	3,987.9
Commercial Portfolio Segment \| 60% to less than 70%
Financing Receivable, Credit Quality Indicator [Line Items]
2025	105.4
2024	15.0
2023	36.4
2022	24.1
2021	18.0
Prior	36.3
Total amortized cost	235.2
Commercial mortgage loans	218.8
Collateral	362.0
Commercial Portfolio Segment \| 70% to less than 80%
Financing Receivable, Credit Quality Indicator [Line Items]
2025	0.0
2024	0.0
2023	59.6
2022	51.0
2021	0.0
Prior	22.8
Total amortized cost	133.4
Commercial mortgage loans	120.9
Collateral	181.0
Commercial Portfolio Segment \| 80% to less than 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2025	10.1
2024	0.0
2023	0.0
2022	61.0
2021	0.0
Prior	0.0
Total amortized cost	71.1
Commercial mortgage loans	64.2
Collateral	88.3
Commercial Portfolio Segment \| 90% to less than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2025	0.0
2024	0.0
2023	0.0
2022	0.0
2021	7.8
Prior	1.9
Total amortized cost	9.7
Commercial mortgage loans	7.6
Collateral	$ 9.8

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