v3.26.1
Investments - Fixed Maturities (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Mar. 31, 2026
Dec. 31, 2025
Jun. 30, 2025
Mar. 31, 2025
Dec. 31, 2024
Available-for-sale securities            
Amortized cost, fixed maturities $ 78,612.0   $ 77,566.0      
Gross unrealized gains, fixed maturities 848.6   1,052.6      
Gross unrealized losses, fixed maturities 5,428.7   5,231.0      
Allowance, fixed maturities 45.6 $ 52.2 26.9 $ 3.1 $ 7.0 $ 18.7
Fair value, fixed maturities [1] 73,986.3   73,360.7      
Amortized cost, excluding portfolio layer method basis adjustment 78,635.7   77,582.9      
Gross unrealized gains, excluding portfolio layer method basis adjustment 824.9   1,035.7      
Gross unrealized losses, excluding portfolio layer method basis adjustment 5,428.7   5,231.0      
Allowance, excluding portfolio layer method basis adjustment 45.6   26.9      
Fair value, excluding portfolio layer method basis adjustment 73,986.3   73,360.7      
Amortized cost, unallocated portfolio layer method basis adjustment (23.7)   (16.9)      
Gross unrealized gains, unallocated portfolio layer method basis adjustment 23.7   16.9      
U.S. government and agencies            
Available-for-sale securities            
Amortized cost, fixed maturities 2,270.0   2,126.2      
Gross unrealized gains, fixed maturities 2.3   9.6      
Gross unrealized losses, fixed maturities 291.3   268.1      
Allowance, fixed maturities   0.1 0.1      
Fair value, fixed maturities 1,981.0   1,867.6      
Non-U.S. governments            
Available-for-sale securities            
Amortized cost, fixed maturities 423.1   554.7      
Gross unrealized gains, fixed maturities 13.4   17.6      
Gross unrealized losses, fixed maturities 39.5   54.6      
Fair value, fixed maturities 397.0   517.7      
States and political subdivisions            
Available-for-sale securities            
Amortized cost, fixed maturities 8,298.1   8,107.8      
Gross unrealized gains, fixed maturities 44.7   42.8      
Gross unrealized losses, fixed maturities 1,020.8   1,011.9      
Fair value, fixed maturities 7,322.0   7,138.7      
Corporate debt securities            
Available-for-sale securities            
Amortized cost, fixed maturities 40,570.9   39,867.6      
Gross unrealized gains, fixed maturities 665.2   777.7      
Gross unrealized losses, fixed maturities 3,185.4   3,072.8      
Allowance, fixed maturities 43.6 50.1 25.0 2.5 6.8 18.5
Fair value, fixed maturities 38,007.1   37,547.5      
Residential mortgage-backed pass-through securities            
Available-for-sale securities            
Amortized cost, fixed maturities 3,769.7   3,868.4      
Gross unrealized gains, fixed maturities 27.8   54.7      
Gross unrealized losses, fixed maturities 134.7   118.0      
Fair value, fixed maturities 3,662.8   3,805.1      
Commercial mortgage-backed securities            
Available-for-sale securities            
Amortized cost, fixed maturities 5,938.5   5,659.6      
Gross unrealized gains, fixed maturities 8.6   19.4      
Gross unrealized losses, fixed maturities 324.8   306.0      
Allowance, fixed maturities 1.7 1.6 1.4 0.3    
Fair value, fixed maturities 5,620.6   5,371.6      
Collateralized debt obligations            
Available-for-sale securities            
Amortized cost, fixed maturities 5,880.3   6,417.4      
Gross unrealized gains, fixed maturities 6.5   14.6      
Gross unrealized losses, fixed maturities 15.5   9.7      
Allowance, fixed maturities       0.1    
Fair value, fixed maturities 5,871.3   6,422.3      
Other debt obligations            
Available-for-sale securities            
Amortized cost, fixed maturities 11,485.1   10,981.2      
Gross unrealized gains, fixed maturities 56.4   99.3      
Gross unrealized losses, fixed maturities 416.7   389.9      
Allowance, fixed maturities 0.3 $ 0.4 0.4 $ 0.2 $ 0.2 $ 0.2
Fair value, fixed maturities 11,124.5   10,690.2      
Fixed maturities            
Available-for-sale securities            
Accrued interest receivable $ 656.9   $ 473.8      
[1] See Note 3, Investments, for further details relating to the amortized cost of fixed maturities, available-for-sale.