Pension and Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2020

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,
	2020			2019			2020			2019
	(Dollars in Millions)
Service cost	$	9.8		$	7.7		$	—		$	—
Interest cost		9.3			9.4			0.1			0.1
Expected return on assets		(15.2	)		(11.9	)		—			—
Amortization of:
Prior service cost (credit)		0.2			—			(0.2	)		(0.2	)
Actuarial loss (gain)		4.2			3.9			—			(0.1	)
Net periodic benefit cost (credit)	$	8.3		$	9.1		$	(0.1	)	$	(0.2	)

	Pension						Postretirement Benefits
	Nine Months Ended September 30,
	2020			2019			2020			2019
	(Dollars in Millions)
Service cost	$	29.4		$	23.1		$	—		$	—
Interest cost		27.8			28.3			0.3			0.4
Expected return on assets		(43.8	)		(35.9	)		—			—
Amortization of:
Prior service cost (credit)		0.5			—			(0.6	)		(0.5	)
Actuarial loss (gain)		10.9			11.9			(0.1	)		(0.4	)
Net periodic benefit cost (credit)	$	24.8		$	27.4		$	(0.4	)	$	(0.5	)