Pension and Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2021			2020			2021			2020
	(Dollars in Millions)
Service cost	$	11.6		$	9.7		$	—		$	—
Interest cost		9.0			9.2			0.1			0.1
Expected return on assets		(17.6	)		(14.6	)		—			—
Amortization of:
Prior service cost (credit)		0.2			0.2			(0.2	)		(0.2	)
Actuarial loss (gain)		3.3			3.3			(0.1	)		—
Net periodic benefit cost (credit)	$	6.5		$	7.8		$	(0.2	)	$	(0.1	)