We sponsor programs that provide retirement benefits to most of our employees. These programs include defined benefit pension plans, defined contribution plans and postretirement healthcare plans. Key terms of our retirement plans are provided in our Annual Report. Our retirement plans' costs for the three-month periods ended August 31 were as follows (in millions):

	2016		2015
Defined benefit pension plans	$	58	$	53
Defined contribution plans		119		102
Postretirement healthcare plans		19		21
	$	196	$	176

Net periodic benefit cost of the pension and postretirement healthcare plans for the three-month periods ended August 31 included the following components (in millions):

	Pension Plans				Postretirement Healthcare Plans
	2016		2015		2016		2015
Service cost	$	180	$	166	$	9	$	10
Interest cost		293		295		10		11
Expected return on plan assets		(386)		(377)		-		-
Amortization of prior service credit and other		(29)		(31)		-		-
	$	58	$	53	$	19	$	21

Contributions to our tax-qualified U.S. domestic pension plans (“U.S. Pension Plans”) for the three-month periods ended August 31 were as follows (in millions):

	2016		2015
Required	$	-	$	6
Voluntary		250		159
	$	250	$	165

In September 2016, we made a required contribution of $250 million to our U.S. Pension Plans. Our U.S. Pension Plans have ample funds to meet expected benefit payments.