Pension and Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2022

Retirement Benefits [Abstract]

Schedule of Components of Net Periodic Benefit Cost (Credit)

The estimated components of the recorded net periodic benefit cost (credit) for pension and postretirement benefits are as follows:

	Pension						Postretirement Benefits
	Three Months Ended June 30,
	2022			2021			2022			2021
	(Dollars in Millions)
Service cost	$	14.0		$	10.6		$	—		$	—
Interest cost		11.9			8.3			0.1			0.1
Expected return on assets		(22.5	)		(16.3	)		—			—
Amortization of:
Prior service cost (credit)		1.4			0.3			(0.2	)		(0.2	)
Actuarial loss (gain)		1.2			2.8			(0.1	)		—
Net periodic benefit cost (credit)	$	6.0		$	5.7		$	(0.2	)	$	(0.1	)

	Pension						Postretirement Benefits
	Six Months Ended June 30,
	2022			2021			2022			2021
	(Dollars in Millions)
Service cost	$	24.0		$	23.0		$	—		$	—
Interest cost		20.6			17.7			0.2			0.2
Expected return on assets		(38.7	)		(35.1	)		—			—
Amortization of:
Prior service cost (credit)		2.5			0.4			(0.4	)		(0.4	)
Actuarial loss (gain)		2.0			6.2			(0.1	)		(0.1	)
Net periodic benefit cost (credit)	$	10.4		$	12.2		$	(0.3	)	$	(0.3	)