BENEFITS

The components of our net periodic pension and Other Post-Retirement Employee Benefits (OPEB) costs for the three and six months ended June 30 were as follows:



	Pension Costs
	Three Months Ended June 30						Six Months Ended June 30
Benefit Plan Cost Components	2015			2014			2015			2014
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	3.9		$	2.3		$	7.8		$	5.0
Interest cost	15.1			17.0			30.3			34.1
Expected return on plan assets	(25.6		)	(24.6		)	(51.4		)	(49.3		)
Amortization of:
Prior service cost	0.5			0.5			1.0			1.0
Actuarial loss	11.4			9.3			23.0			18.4
Net Periodic Benefit Cost	$	5.3		$	4.5		$	10.7		$	9.2



	OPEB Costs
	Three Months Ended June 30						Six Months Ended June 30
Benefit Plan Cost Components	2015			2014			2015			2014
	(Millions of Dollars)
Net Periodic Benefit Cost
Service cost	$	2.1		$	2.1		$	4.7		$	4.3
Interest cost	3.9			4.4			8.1			8.9
Expected return on plan assets	(5.9		)	(6.0		)	(11.8		)	(11.9		)
Amortization of:
Transition obligation	—			—			—			—
Prior service (credit)	(0.3		)	(0.4		)	(0.6		)	(0.9		)
Actuarial loss	0.5			0.4			1.0			0.6
Net Periodic Benefit Cost	$	0.3		$	0.5		$	1.4		$	1.0

We contributed $100.0 million to our qualified pension plan during the first six months of 2015. No such contribution was made during the first six months of 2014.

Postemployment Benefits: Postemployment benefits provided to former or inactive employees are recognized when an event occurs. The estimated liability for such benefits was $7.0 million as of June 30, 2015 and $3.3 million as of December 31, 2014.