v3.26.3
Employee Benefits - Components of 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
Retirement Plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost $ 0.4 $ 0.5 $ 1.3 $ 1.4
Interest cost 0.8 1.0 2.5 2.9
Expected return on plan assets (0.9) (1.1) (2.9) (3.2)
Amortization of unrecognized net loss     0.1 0.1
Settlement charge 0.0 0.2 0.2 0.7
Amortization of prior service cost 0.0 0.0 0.0 0.0
Regulatory asset decrease 0.4 0.3 0.5 0.4
Net periodic benefit cost (credit) 0.7 0.9 1.7 2.3
PBOP        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 0.0 0.0 0.0 0.0
Interest cost 0.4 0.3 1.1 0.9
Expected return on plan assets (0.7) (0.7) (2.1) (2.1)
Amortization of unrecognized net loss     0.0 0.0
Settlement charge 0.0 0.0 0.0 0.0
Amortization of prior service cost 0.4 0.0 1.2 0.0
Regulatory asset decrease 0.0 0.0 0.0 0.0
Net periodic benefit cost (credit) $ 0.1 $ (0.4) $ 0.2 $ (1.2)