We have defined benefit pension plans and other postretirement benefit plans for certain U.S. and non-U.S. employees. Certain plans have been frozen for salaried and non-union hourly employees at various times in the past, although some employees meeting certain criteria are still accruing benefits. In addition, we participate in several multiemployer pension plans (“MEPP” or “MEPPs”) that provide retirement benefits to certain union employees in accordance with various collective bargaining agreements. We also have supplemental executive retirement plans and other non-qualified defined benefit pension plans that provide unfunded supplemental retirement benefits to certain of our current and former executives. See “Note 4. Retirement Plans” of the Notes to Consolidated Financial Statements section in Exhibit 99.1 of the May 9, 2019 Form 8-K for more information regarding our involvement with retirement plans.

In connection with the KapStone Acquisition, the KapStone Paper and Packaging Corporation Defined Benefit Retirement Plan assigned the role of plan sponsor to WestRock. On December 31, 2018, WestRock merged the KapStone Paper and Packaging Corporation Defined Benefit Retirement Plan into the WestRock Company Consolidated Pension Plan. Upon the merger, the terms and provisions of the legacy KapStone plan were incorporated into the WestRock Company Consolidated Pension Plan.

In the normal course of business, we evaluate our potential exposure to MEPPs, including with respect to potential withdrawal liabilities. During the three months ended December 31, 2017, we submitted formal notification to withdraw from the Pace Industry Union-Management Pension Fund (“PIUMPF”) and recorded an estimated withdrawal liability of $180.0 million at that time. The estimated withdrawal liability assumed payments over 20 years, discounted at a credit adjusted risk-free rate. We expect that PIUMPF’s demand related to the withdrawal will include both a payment for withdrawal liability and for our proportionate share of PIUMPF’s accumulated funding deficiency. We reserve the right to challenge any portion of the demand, including any portion related to the accumulated funding deficiency. The estimated withdrawal liability noted above excludes the potential impact of a future mass withdrawal of other employers from PIUMPF, which is not considered probable or reasonably estimable at this time. Due to the absence of specific information regarding matters such as PIUMPF’s current financial situation, our estimate is subject to revision. In addition, in the third quarter of fiscal 2018, we submitted formal notification to withdraw from the Central States, Southeast and Southwest Areas Pension Plan and recorded an estimated withdrawal liability of $4.2 million on a discounted basis. In the third quarter of fiscal 2019, in a separate matter, we recorded a $1.7 million reduction to a previously recorded MEPP withdrawal liability. It is reasonably possible that we may incur withdrawal liabilities with respect to certain other MEPPs in connection with such withdrawals. Our estimate of any such withdrawal liability, both individually and in the aggregate, is not material for the remaining plans in which we participate. At June 30, 2019 and September 30, 2018, we had withdrawal liabilities recorded of $240.5 million and $247.8 million, respectively.

See “Note 4. Retirement Plans — Multiemployer Plans” of the Notes to Consolidated Financial Statements section in Exhibit 99.1 of the May 9, 2019 Form 8-K for more information regarding our involvement with MEPPs.

The following table presents a summary of the components of net pension (income) cost (in millions):

	Three Months Ended						Nine Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Service cost	$	10.2		$	9.4		$	32.5		$	33.5
Interest cost		58.8			51.5			174.0			153.7
Expected return on plan assets		(85.9	)		(82.1	)		(254.7	)		(246.7	)
Amortization of net actuarial loss		6.3			6.7			18.7			15.9
Amortization of prior service cost		1.3			1.3			3.9			3.5
Curtailment loss		0.1			—			1.0			—
Company defined benefit plan income		(9.2	)		(13.2	)		(24.6	)		(40.1	)
Multiemployer pension withdrawals		(1.7	)		4.2			(1.7	)		184.2
Multiemployer and other plans		0.2			0.2			0.5			1.3
Net pension (income) cost	$	(10.7	)	$	(8.8	)	$	(25.8	)	$	145.4

The Condensed Consolidated Statements of Income line item “Pension and other postretirement non-service income” is equal to the non-service elements of our “Company defined benefit plan income” and our “Net postretirement cost” set forth in this Note 5. Retirement Plans.

During the three and nine months ended June 30, 2019, we made contributions to our qualified and supplemental defined benefit pension plans of $6.6 million and $16.1 million, respectively, and for the three and nine months ended June 30, 2018, we made contributions of $10.8 million and $31.5 million, respectively.

We maintain other postretirement benefit plans that provide certain health care and life insurance benefits for certain salaried and hourly employees who meet specified age and service requirements as defined by the plans. The following table presents a summary of the components of the net postretirement cost (in millions):

	Three Months Ended						Nine Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Service cost	$	0.2		$	0.4		$	0.8		$	1.2
Interest cost		1.9			2.1			5.8			6.1
Amortization of net actuarial (gain) loss		(0.7	)		0.3			(1.5	)		0.2
Amortization of prior service credit		(0.7	)		(1.1	)		(2.1	)		(3.2	)
Net postretirement cost	$	0.7		$	1.7		$	3.0		$	4.3

During the three and nine months ended June 30, 2019, we funded an aggregate of $2.2 million and $6.6 million, respectively, and for the three and nine months ended June 30, 2018, we funded an aggregate of $2.3 million and $7.1 million, respectively, to our other postretirement benefit plans.