Postretirement Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2025

Retirement Benefits [Abstract]

Schedule of Debt Securities, Trading, and Equity Securities, FV-NI

The following table summarizes, by major security type, our marketable securities that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy:

	Fair Value of Deferred Compensation Plan as of June 30, 2025
(Dollars in millions)	Adjusted Cost		Unrealized Gains		Unrealized Losses		Fair Value
Level 1 Securities:
Mutual funds	$	4.0	$	0.7	$	(0.1)	$	4.6
Level 2 Securities:
Fixed income funds	$	0.1	$	—	$	—	$	0.1
Total	$	4.1	$	0.7	$	(0.1)	$	4.7

	Fair Value of Deferred Compensation Plan as of December 31, 2024
(Dollars in millions)	Adjusted Cost		Unrealized Gains		Unrealized Losses		Fair Value
Level 1 Securities:
Mutual funds	$	4.6	$	0.5	$	—	$	5.1
Level 2 Securities:
Fixed income funds	$	0.2	$	—	$	—	$	0.2
Total	$	4.8	$	0.5	$	—	$	5.3