v3.26.3
Pension and Postretirement Benefit Costs (Tables)
 9 Months Ended
Sep. 30, 2026
Retirement Benefits [Abstract]  
Schedule of Net Benefit Costs
Net periodic postretirement benefit credit included the following components:
Three Months Ended September 30,Nine Months Ended September 30,
2026202520262025
(Dollars in millions)
Service cost for benefits earned$— $0.1 $0.1 $0.3 
Interest cost on accumulated postretirement benefit obligation1.3 1.9 4.6 5.8 
Expected return on plan assets— (0.1)(0.1)(0.3)
Amortization of prior service credit(14.3)(10.2)(20.0)(30.6)
Net actuarial gain(3.3)— (3.3)— 
Net periodic postretirement benefit credit$(16.3)$(8.3)$(18.7)$(24.8)