Employee Benefit Plans and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2018

Compensation And Retirement Disclosure [Abstract]

Components of Net Periodic Benefit Costs

The components of net periodic benefit cost for our pension plans were as follows (dollars in millions):

	Pension Plans
	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Service cost	$	6.2		$	6.1		$	12.4		$	12.2
Interest cost		10.6			10.4			21.3			20.8
Expected return on plan assets		(14.2	)		(13.5	)		(28.3	)		(27.0	)
Net amortization of unrecognized amounts
Prior service cost		1.8			1.5			3.4			3.0
Actuarial loss		2.3			1.9			4.6			3.7
Net periodic benefit cost	$	6.7		$	6.4		$	13.4		$	12.7

The components of net periodic benefit cost for our postretirement plans were as follows (dollars in millions):

	Postretirement Plans
	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Service cost	$	0.1		$	0.1		$	0.2		$	0.2
Interest cost		0.1			0.2			0.2			0.3
Net amortization of unrecognized amounts
Prior service cost		(0.1	)		(0.1	)		(0.1	)		(0.1	)
Net periodic benefit cost	$	0.1		$	0.2		$	0.3		$	0.4