v3.26.3
Investments - Debt Securities (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Debt securities, available for sale    
Cost or amortized cost $ 5,523.9 $ 5,118.3
Gross unrealized gains 3.3 66.2
Gross unrealized losses (164.3) (13.3)
Net foreign currency gains (losses) 1.9 (2.6)
Fair value 5,364.8 5,168.6
Debt securities, trading    
Cost or amortized cost 80.6 114.6
Gross unrealized gains 0.1 0.5
Gross unrealized losses (25.4) (24.8)
Net foreign currency gains (losses) 0.0 0.0
Fair value 55.3 90.3
Asset-backed securities    
Debt securities, available for sale    
Cost or amortized cost 782.2 917.1
Gross unrealized gains 1.3 7.3
Gross unrealized losses (13.5) (3.3)
Net foreign currency gains (losses) 0.0 0.0
Fair value 770.0 921.1
Debt securities, trading    
Cost or amortized cost 7.7 8.3
Gross unrealized gains 0.0 0.0
Gross unrealized losses (2.7) (2.4)
Net foreign currency gains (losses) 0.0 0.0
Fair value 5.0 5.9
Residential mortgage-backed securities    
Debt securities, available for sale    
Cost or amortized cost 1,110.9 950.1
Gross unrealized gains 0.3 17.7
Gross unrealized losses (44.6) (4.7)
Net foreign currency gains (losses) 0.0 0.0
Fair value 1,066.6 963.1
Debt securities, trading    
Cost or amortized cost 30.7 50.7
Gross unrealized gains 0.0 0.1
Gross unrealized losses (5.8) (5.8)
Net foreign currency gains (losses) 0.0 0.0
Fair value 24.9 45.0
Commercial mortgage-backed securities    
Debt securities, available for sale    
Cost or amortized cost 253.4 231.3
Gross unrealized gains 0.2 3.1
Gross unrealized losses (6.1) (2.5)
Net foreign currency gains (losses) 0.0 0.0
Fair value 247.5 231.9
Debt securities, trading    
Cost or amortized cost 23.0 34.6
Gross unrealized gains 0.0 0.4
Gross unrealized losses (3.5) (3.1)
Net foreign currency gains (losses) 0.0 0.0
Fair value 19.5 31.9
Corporate debt securities    
Debt securities, available for sale    
Cost or amortized cost 2,453.9 2,170.8
Gross unrealized gains 1.5 32.3
Gross unrealized losses (76.5) (2.4)
Net foreign currency gains (losses) 1.2 (2.5)
Fair value 2,380.1 2,198.2
Debt securities, trading    
Cost or amortized cost 16.2 17.1
Gross unrealized gains 0.1 0.0
Gross unrealized losses (13.4) (13.4)
Net foreign currency gains (losses) 0.0 0.0
Fair value 2.9 3.7
U.S. government and government agency    
Debt securities, available for sale    
Cost or amortized cost 903.8 830.5
Gross unrealized gains 0.0 5.6
Gross unrealized losses (23.3) (0.4)
Net foreign currency gains (losses) 0.3 0.0
Fair value 880.8 835.7
Debt securities, trading    
Cost or amortized cost 3.0 3.9
Gross unrealized gains 0.0 0.0
Gross unrealized losses 0.0 (0.1)
Net foreign currency gains (losses) 0.0 0.0
Fair value 3.0 3.8
Non-U.S. government and government agency    
Debt securities, available for sale    
Cost or amortized cost 19.7 18.5
Gross unrealized gains 0.0 0.2
Gross unrealized losses (0.3) 0.0
Net foreign currency gains (losses) 0.4 (0.1)
Fair value $ 19.8 $ 18.6