Pension and Postretirement Benefits (Tables)

6 Months Ended

Jun. 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 June 30,
	2023			2022			2023			2022
	(Dollars in Millions)
Service cost	$	9.3		$	14.0		$	—		$	—
Interest cost		14.6			11.9			0.2			0.1
Expected return on assets		(20.3	)		(22.5	)		—			—
Amortization of:
Prior service cost (credit)		1.7			1.4			(0.1	)		(0.2	)
Actuarial loss (gain)		0.2			1.2			(0.2	)		(0.1	)
Net periodic benefit cost (credit)	$	5.5		$	6.0		$	(0.1	)	$	(0.2	)

	Pension						Postretirement Benefits
	Six Months Ended June 30,
	2023			2022			2023			2022
	(Dollars in Millions)
Service cost	$	16.4		$	24.0		$	—		$	—
Interest cost		25.7			20.6			0.2			0.2
Expected return on assets		(35.7	)		(38.7	)		—			—
Amortization of:
Prior service cost (credit)		2.9			2.5			(0.1	)		(0.4	)
Actuarial loss (gain)		0.3			2.0			(0.3	)		(0.1	)
Net periodic benefit cost (credit)	$	9.6		$	10.4		$	(0.2	)	$	(0.3	)