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Retirement Plans (Tables)
 9 Months Ended
Sep. 30, 2025
Retirement Benefits, Description [Abstract]  
Schedule of Components of Net Periodic Benefit Cost
The components of net periodic benefit cost for the three and nine months ended September 30 were as follows.
COMPONENTS OF NET PERIODIC BENEFIT COST
 Three Months Ended September 30,Nine Months Ended September 30,
(Dollars in millions)2025202420252024
Components of net periodic benefit cost
Interest cost$9 $8 $25 $25 
Expected return on plan assets(9)(8)(25)(24)
Amortization of unrecognized:
Actuarial (gain) loss2 3 8 9 
Net periodic benefit cost$2 $3 $8 $10