Pension and Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2021

Compensation And Retirement Disclosure [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 September 30,
	2021			2020			2021			2020
	(Dollars in Millions)
Service cost	$	11.6		$	9.8		$	—		$	—
Interest cost		8.9			9.3			0.1			0.1
Expected return on assets		(17.7	)		(15.2	)		—			—
Amortization of:
Prior service cost (credit)		0.2			0.2			(0.2	)		(0.2	)
Actuarial loss		3.0			4.2			—			—
Net periodic benefit cost (credit)	$	6.0		$	8.3		$	(0.1	)	$	(0.1	)

	Pension						Postretirement Benefits
	Nine Months Ended September 30,
	2021			2020			2021			2020
	(Dollars in Millions)
Service cost	$	34.7		$	29.4		$	—		$	—
Interest cost		26.7			27.8			0.2			0.3
Expected return on assets		(52.8	)		(43.8	)		—			—
Amortization of:
Prior service cost (credit)		0.5			0.5			(0.5	)		(0.6	)
Actuarial loss (gain)		9.2			10.9			(0.1	)		(0.1	)
Net periodic benefit cost (credit)	$	18.3		$	24.8		$	(0.4	)	$	(0.4	)