Pension and Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2023

Retirement Benefits [Abstract]

Schedule of Components of Net Periodic Benefit Cost (Credit)

The net periodic benefit cost (credit) for pension and postretirement benefits includes the following components:

	Pension						Postretirement Benefits
	Three Months Ended September 30,
	2023			2022			2023			2022
	(Dollars in Millions)
Service cost	$	8.2		$	12.0		$	—		$	—
Interest cost		12.8			10.3			0.1			0.1
Expected return on assets		(17.9	)		(19.3	)		—			—
Amortization of:
Prior service cost (credit)		1.5			1.3			(0.1	)		(0.2	)
Actuarial loss (gain)		0.2			1.0			(0.1	)		(0.1	)
Settlement charge		—			4.5			—			—
Net periodic benefit cost (credit)	$	4.8		$	9.8		$	(0.1	)	$	(0.2	)

	Pension						Postretirement Benefits
	Nine Months Ended September 30,
	2023			2022			2023			2022
	(Dollars in Millions)
Service cost	$	24.6		$	36.1		$	—		$	—
Interest cost		38.5			30.9			0.4			0.2
Expected return on assets		(53.6	)		(58.0	)		—			—
Amortization of:
Prior service cost (credit)		4.4			3.7			(0.2	)		(0.5	)
Actuarial loss (gain)		0.5			3.0			(0.5	)		(0.2	)
Settlement charge		—			4.5			—			—
Net periodic benefit cost (credit)	$	14.4		$	20.2		$	(0.3	)	$	(0.5	)