Pension and Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2020			2019			2020			2019
	(Dollars in Millions)
Service cost	$	9.7		$	7.9		$	—		$	—
Interest cost		9.2			9.4			0.1			0.1
Expected return on assets		(14.6	)		(12.0	)		—			—
Amortization of:
Prior service cost (credit)		0.2			—			(0.2	)		(0.2	)
Actuarial loss (gain)		3.3			3.9			—			(0.1	)
Net periodic benefit cost (credit)	$	7.8		$	9.2		$	(0.1	)	$	(0.2	)