FAIR VALUE MEASUREMENTS - FAIR VALUE MEASUREMENTS OF FINANCIAL INSTRUMENTS MEASURED ON A RECURRING BASIS - FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Other invested assets:
Company-owned life insurance	$ 212.6	$ 202.9
Cash and cash equivalents:
Held by variable interest entities	341.0	114.5
Key Employee
Other invested assets:
Company-owned life insurance	189.5	100.1
Fair value, Measurements, Recurring \| Estimated fair value
Assets:
Mortgage loans	2,376.0	1,926.9
Policy loans	135.3	128.5
Other invested assets:
Company-owned life insurance	402.1	303.0
Cash and cash equivalents:
Unrestricted	1,656.7	774.5
Held by variable interest entities	341.0	114.5
Liabilities:
Policyholder account balances	17,615.8	15,222.5
Investment borrowings	2,189.8	2,190.2
Borrowings related to variable interest entities	499.0	814.8
Notes payable – direct corporate obligations	1,837.9	1,097.3
Fair value, Measurements, Recurring \| Total amortized cost
Assets:
Mortgage loans	2,506.3	2,064.1
Policy loans	135.3	128.5
Other invested assets:
Company-owned life insurance	402.1	303.0
Cash and cash equivalents:
Unrestricted	1,656.7	774.5
Held by variable interest entities	341.0	114.5
Liabilities:
Policyholder account balances	17,615.8	15,222.5
Investment borrowings	2,188.8	2,189.3
Borrowings related to variable interest entities	497.6	820.8
Notes payable – direct corporate obligations	1,833.5	1,140.5
Fair value, Measurements, Recurring \| Quoted prices in active markets for identical assets or liabilities (Level 1)
Assets:
Mortgage loans	0.0	0.0
Policy loans	0.0	0.0
Other invested assets:
Company-owned life insurance	0.0	0.0
Cash and cash equivalents:
Unrestricted	1,656.7	774.5
Held by variable interest entities	341.0	114.5
Liabilities:
Policyholder account balances	0.0	0.0
Investment borrowings	0.0	0.0
Borrowings related to variable interest entities	0.0	0.0
Notes payable – direct corporate obligations	0.0	0.0
Fair value, Measurements, Recurring \| Significant other observable inputs (Level 2)
Assets:
Mortgage loans	0.0	0.0
Policy loans	0.0	0.0
Other invested assets:
Company-owned life insurance	402.1	303.0
Cash and cash equivalents:
Unrestricted	0.0	0.0
Held by variable interest entities	0.0	0.0
Liabilities:
Policyholder account balances	0.0	0.0
Investment borrowings	2,189.8	2,190.2
Borrowings related to variable interest entities	499.0	814.8
Notes payable – direct corporate obligations	1,837.9	1,097.3
Fair value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets:
Mortgage loans	2,376.0	1,926.9
Policy loans	135.3	128.5
Other invested assets:
Company-owned life insurance	0.0	0.0
Cash and cash equivalents:
Unrestricted	0.0	0.0
Held by variable interest entities	0.0	0.0
Liabilities:
Policyholder account balances	17,615.8	15,222.5
Investment borrowings	0.0	0.0
Borrowings related to variable interest entities	0.0	0.0
Notes payable – direct corporate obligations	$ 0.0	$ 0.0

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