v3.26.1
FAIR VALUE MEASUREMENTS - MEASUREMENTS BY INPUT LEVEL (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Assets:      
Total fixed maturities, available for sale $ 24,495.7 $ 23,886.8  
Equity securities - corporate securities 337.2 389.2  
Total trading securities 258.6 294.8  
Investments held by variable interest entities - corporate securities 292.3 293.0  
Derivatives 294.2 323.5  
Residual tranches 4.5 4.2  
Total other invested assets 298.7 327.7  
Assets held in separate accounts 3.0 2.8  
Total assets carried at fair value by category 25,667.9 25,172.3  
Equity securities measured at net asset value 17.6 22.0  
Total assets carried at fair value 25,685.5 25,194.3  
Liabilities:      
Market risk benefit liability 50.6 48.1 $ 63.8
Embedded derivatives associated with fixed indexed annuity products 1,676.7 1,600.6  
Total liabilities carried at fair value 1,727.3 1,648.7  
Corporate securities      
Assets:      
Total fixed maturities, available for sale 13,521.5 13,262.5  
Equity securities - corporate securities 319.6 367.2  
United States Treasury securities and obligations of United States government corporations and agencies      
Assets:      
Total fixed maturities, available for sale 178.9 177.1  
States and political subdivisions      
Assets:      
Total fixed maturities, available for sale 2,903.1 2,954.7  
Foreign governments      
Assets:      
Total fixed maturities, available for sale 121.6 120.5  
Asset-backed securities      
Assets:      
Total fixed maturities, available for sale 1,946.9 1,747.3  
Total trading securities 32.9 38.7  
Agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 717.3 849.5  
Total trading securities 78.4 97.5  
Non-agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 1,426.2 1,585.7  
Total trading securities 33.2 44.2  
Collateralized loan obligations      
Assets:      
Total fixed maturities, available for sale 1,597.8 1,142.5  
Total trading securities 9.3 9.7  
Commercial mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 2,082.4 2,047.0  
Total trading securities 104.8 104.7  
Total fixed maturities, available for sale      
Assets:      
Total fixed maturities, available for sale 24,495.7 23,886.8  
Quoted prices in active markets for identical assets or liabilities (Level 1)      
Assets:      
Total trading securities 0.0 0.0  
Investments held by variable interest entities - corporate securities 0.0 0.0  
Derivatives 0.0 0.0  
Residual tranches 0.0 0.0  
Total other invested assets 0.0 0.0  
Assets held in separate accounts 0.0 0.0  
Total assets carried at fair value by category 174.7 176.5  
Liabilities:      
Market risk benefit liability 0.0 0.0  
Embedded derivatives associated with fixed indexed annuity products 0.0 0.0  
Total liabilities carried at fair value 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Corporate securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Equity securities - corporate securities 174.7 176.5  
Quoted prices in active markets for identical assets or liabilities (Level 1) | United States Treasury securities and obligations of United States government corporations and agencies      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | States and political subdivisions      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Foreign governments      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Asset-backed securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Non-agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Collateralized loan obligations      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Commercial mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Quoted prices in active markets for identical assets or liabilities (Level 1) | Total fixed maturities, available for sale      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Significant other observable inputs (Level 2)      
Assets:      
Total trading securities 258.6 294.8  
Investments held by variable interest entities - corporate securities 292.3 293.0  
Derivatives 294.2 323.5  
Residual tranches 0.0 0.0  
Total other invested assets 294.2 323.5  
Assets held in separate accounts 3.0 2.8  
Total assets carried at fair value by category 25,166.8 24,746.1  
Liabilities:      
Market risk benefit liability 0.0 0.0  
Embedded derivatives associated with fixed indexed annuity products 0.0 0.0  
Total liabilities carried at fair value 0.0 0.0  
Significant other observable inputs (Level 2) | Corporate securities      
Assets:      
Total fixed maturities, available for sale 13,348.5 13,130.7  
Equity securities - corporate securities 71.4 117.0  
Significant other observable inputs (Level 2) | United States Treasury securities and obligations of United States government corporations and agencies      
Assets:      
Total fixed maturities, available for sale 178.9 177.1  
Significant other observable inputs (Level 2) | States and political subdivisions      
Assets:      
Total fixed maturities, available for sale 2,903.1 2,954.7  
Significant other observable inputs (Level 2) | Foreign governments      
Assets:      
Total fixed maturities, available for sale 121.6 120.5  
Significant other observable inputs (Level 2) | Asset-backed securities      
Assets:      
Total fixed maturities, available for sale 1,903.8 1,710.8  
Total trading securities 32.9 38.7  
Significant other observable inputs (Level 2) | Agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 717.3 849.5  
Total trading securities 78.4 97.5  
Significant other observable inputs (Level 2) | Non-agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 1,397.4 1,585.7  
Total trading securities 33.2 44.2  
Significant other observable inputs (Level 2) | Collateralized loan obligations      
Assets:      
Total fixed maturities, available for sale 1,597.8 1,142.5  
Total trading securities 9.3 9.7  
Significant other observable inputs (Level 2) | Commercial mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 2,078.9 2,043.5  
Total trading securities 104.8 104.7  
Significant other observable inputs (Level 2) | Total fixed maturities, available for sale      
Assets:      
Total fixed maturities, available for sale 24,247.3 23,715.0  
Significant unobservable inputs  (Level 3)      
Assets:      
Total trading securities 0.0 0.0  
Investments held by variable interest entities - corporate securities 0.0 0.0  
Derivatives 0.0 0.0  
Residual tranches 4.5 4.2  
Total other invested assets 4.5 4.2  
Assets held in separate accounts 0.0 0.0  
Total assets carried at fair value by category 326.4 249.7  
Liabilities:      
Market risk benefit liability 50.6 48.1  
Embedded derivatives associated with fixed indexed annuity products 1,676.7 1,600.6  
Total liabilities carried at fair value 1,727.3 1,648.7  
Significant unobservable inputs  (Level 3) | Corporate securities      
Assets:      
Total fixed maturities, available for sale 173.0 131.8  
Equity securities - corporate securities 73.5 73.7  
Significant unobservable inputs  (Level 3) | United States Treasury securities and obligations of United States government corporations and agencies      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Significant unobservable inputs  (Level 3) | States and political subdivisions      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Significant unobservable inputs  (Level 3) | Foreign governments      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Significant unobservable inputs  (Level 3) | Asset-backed securities      
Assets:      
Total fixed maturities, available for sale 43.1 36.5  
Total trading securities 0.0 0.0  
Significant unobservable inputs  (Level 3) | Agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Significant unobservable inputs  (Level 3) | Non-agency residential mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 28.8 0.0  
Total trading securities 0.0 0.0  
Significant unobservable inputs  (Level 3) | Collateralized loan obligations      
Assets:      
Total fixed maturities, available for sale 0.0 0.0  
Total trading securities 0.0 0.0  
Significant unobservable inputs  (Level 3) | Commercial mortgage-backed securities      
Assets:      
Total fixed maturities, available for sale 3.5 3.5  
Total trading securities 0.0 0.0  
Significant unobservable inputs  (Level 3) | Total fixed maturities, available for sale      
Assets:      
Total fixed maturities, available for sale $ 248.4 $ 171.8