v3.26.3
Investments - Fixed Maturities (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Jun. 30, 2026
Dec. 31, 2025
Sep. 30, 2025
Jun. 30, 2025
Dec. 31, 2024
Available-for-sale securities            
Amortized cost, fixed maturities $ 78,155.3   $ 77,566.0      
Gross unrealized gains, fixed maturities 286.1   1,052.6      
Gross unrealized losses, fixed maturities 7,881.0   5,231.0      
Allowance, fixed maturities 44.8 $ 45.6 26.9 $ 18.7 $ 3.1 $ 18.7
Fair value, fixed maturities [1] 70,515.6   73,360.7      
Amortized cost, excluding portfolio layer method basis adjustment 78,199.3   77,582.9      
Gross unrealized gains, excluding portfolio layer method basis adjustment 242.1   1,035.7      
Gross unrealized losses, excluding portfolio layer method basis adjustment 7,881.0   5,231.0      
Allowance, excluding portfolio layer method basis adjustment 44.8   26.9      
Fair value, excluding portfolio layer method basis adjustment 70,515.6   73,360.7      
Amortized cost, unallocated portfolio layer method basis adjustment (44.0)   (16.9)      
Gross unrealized gains, unallocated portfolio layer method basis adjustment 44.0   16.9      
U.S. government and agencies            
Available-for-sale securities            
Amortized cost, fixed maturities 2,609.4   2,126.2      
Gross unrealized gains, fixed maturities     9.6      
Gross unrealized losses, fixed maturities 418.9   268.1      
Allowance, fixed maturities     0.1      
Fair value, fixed maturities 2,190.5   1,867.6      
Non-U.S. governments            
Available-for-sale securities            
Amortized cost, fixed maturities 411.4   554.7      
Gross unrealized gains, fixed maturities 8.1   17.6      
Gross unrealized losses, fixed maturities 58.5   54.6      
Fair value, fixed maturities 361.0   517.7      
States and political subdivisions            
Available-for-sale securities            
Amortized cost, fixed maturities 8,289.2   8,107.8      
Gross unrealized gains, fixed maturities 0.1   42.8      
Gross unrealized losses, fixed maturities 1,505.4   1,011.9      
Fair value, fixed maturities 6,783.9   7,138.7      
Corporate debt securities            
Available-for-sale securities            
Amortized cost, fixed maturities 38,914.6   39,867.6      
Gross unrealized gains, fixed maturities 199.2   777.7      
Gross unrealized losses, fixed maturities 4,571.7   3,072.8      
Allowance, fixed maturities 40.6 43.6 25.0 17.3 2.5 18.5
Fair value, fixed maturities 34,501.5   37,547.5      
Residential mortgage-backed pass-through securities            
Available-for-sale securities            
Amortized cost, fixed maturities 3,663.6   3,868.4      
Gross unrealized gains, fixed maturities 0.8   54.7      
Gross unrealized losses, fixed maturities 265.6   118.0      
Fair value, fixed maturities 3,398.8   3,805.1      
Commercial mortgage-backed securities            
Available-for-sale securities            
Amortized cost, fixed maturities 6,049.1   5,659.6      
Gross unrealized gains, fixed maturities 3.1   19.4      
Gross unrealized losses, fixed maturities 410.0   306.0      
Allowance, fixed maturities 3.9 1.7 1.4 1.1 0.3  
Fair value, fixed maturities 5,638.3   5,371.6      
Collateralized debt obligations            
Available-for-sale securities            
Amortized cost, fixed maturities 5,803.4   6,417.4      
Gross unrealized gains, fixed maturities 5.5   14.6      
Gross unrealized losses, fixed maturities 10.1   9.7      
Allowance, fixed maturities         0.1  
Fair value, fixed maturities 5,798.8   6,422.3      
Other debt obligations            
Available-for-sale securities            
Amortized cost, fixed maturities 12,458.6   10,981.2      
Gross unrealized gains, fixed maturities 25.3   99.3      
Gross unrealized losses, fixed maturities 640.8   389.9      
Allowance, fixed maturities 0.3 $ 0.3 0.4 $ 0.3 $ 0.2 $ 0.2
Fair value, fixed maturities 11,842.8   10,690.2      
Fixed maturities            
Available-for-sale securities            
Accrued interest receivable $ 686.3   $ 473.8      
[1] See Note 4, Investments, for further details relating to the amortized cost of fixed maturities, available-for-sale.