v3.26.3
Employee and Agent Benefits - Net Periodic Benefit Cost (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Pension benefits        
Components of Net Periodic Benefit Cost (Income)        
Service cost $ 15.8 $ 14.8 $ 47.3 $ 44.5
Interest cost $ 43.2 $ 43.4 $ 129.5 $ 130.2
Interest cost, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Expected return on plan assets $ (45.9) $ (43.0) $ (137.7) $ (129.0)
Expected return on plan assets, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Amortization of prior service benefit $ (3.7) $ (3.9) $ (11.2) $ (11.4)
Amortization of prior service (benefit) cost, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Recognized net actuarial (gain) loss $ 6.7 $ 8.7 $ 20.0 $ 26.1
Recognized net actuarial (gain) loss, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Settlement     $ 2.6  
Net periodic benefit cost (income) $ 16.1 $ 20.0 50.5 $ 60.4
Other postretirement benefits        
Components of Net Periodic Benefit Cost (Income)        
Interest cost $ 0.7 $ 0.8 $ 2.1 $ 2.3
Interest cost, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Expected return on plan assets $ (1.2) $ (1.2) $ (3.7) $ (3.5)
Expected return on plan assets, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Amortization of prior service benefit $ (0.3) $ (0.2) $ (0.8) $ (0.8)
Amortization of prior service (benefit) cost, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Recognized net actuarial (gain) loss $ (0.5) $ (0.4) $ (1.5) $ (1.1)
Recognized net actuarial (gain) loss, location on consolidated statements of operations Operating expenses Operating expenses Operating expenses Operating expenses
Net periodic benefit cost (income) $ (1.3) $ (1.0) $ (3.9) $ (3.1)