The components of net periodic benefit cost for defined benefit pension plans are summarized in the following table:



		Three Months Ended September 30,						Nine Months Ended September 30,
(Dollars in millions)	Location	2018			2017			2018			2017
Service cost	Personnel expense	$	59		$	47		$	179		$	152
Interest cost	Other expense	50			48			150			144
Estimated return on plan assets	Other expense	(112		)	(93		)	(336		)	(278		)
Amortization and other	Other expense	21			18			60			57
Net periodic benefit cost		$	18		$	20		$	53		$	75

BB&T makes contributions to the qualified pension plans in amounts between the minimum required for funding and the maximum deductible for federal income tax purposes. Discretionary contributions totaling $169 million were made during the nine months ended September 30, 2018. There are no required contributions for the remainder of 2018.