11.	Employee Benefit Plans and Other Postretirement Benefits

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

	Pension Plans
	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Service cost	$	5.8		$	6.2		$	18.0		$	18.4
Interest cost		10.4			10.2			31.1			30.6
Expected return on plan assets		(13.5	)		(12.3	)		(40.5	)		(37.1	)
Net amortization of unrecognized amounts
Prior service cost		1.4			1.4			4.4			4.3
Actuarial loss		1.9			1.5			5.7			4.3
Net periodic benefit cost	$	6.0		$	7.0		$	18.7		$	20.5

PCA makes pension plan contributions that are sufficient to fund its actuarially determined costs, generally equal to the minimum amounts required by the Employee Retirement Income Security Act (ERISA). From time to time, PCA may make additional discretionary contributions based on the funded status of the plans, tax deductibility, income from operations, and other factors. During the three and nine months ended September 30, 2017 and 2016 payments to our nonqualified pension plans were insignificant. For the three and nine months ended September 30, 2017, we made contributions of $36.2 million and $42.1 million, respectively, to our qualified pension plans, which exceeded our 2017 minimum pension contributions of $8.0. We made contributions of $49.7 million and $53.4 million to our qualified plans during the three and nine months ended September 30, 2016 .

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

	Postretirement Plans
	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Service cost	$	0.1		$	0.1		$	0.2		$	0.5
Interest cost		0.2			0.1			0.5			0.5
Net amortization of unrecognized amounts
Prior service cost		(0.1	)		(0.1	)		(0.1	)		(0.1	)
Actuarial income		(0.1	)		—			(0.1	)		(0.4	)
Net periodic benefit cost	$	0.1		$	0.1		$	0.5		$	0.5