EMPLOYEE BENEFIT PLANS (Notes)

6 Months Ended

Jun. 30, 2018

Employee Benefit Plans [Line Items]

EMPLOYEE BENEFIT PLANS

9. EMPLOYEE BENEFIT PLANS

The following tables set forth the components of net periodic benefit cost for our pension and other postemployment benefit plans for the periods indicated:

	Pension Benefits
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	3,230		$	3,044		$	6,460		$	6,088
Interest cost (a)	9,200			10,113			18,400			20,226
Expected return on assets (a)	(15,145		)	(14,624		)	(30,290		)	(29,248		)
Amortization of net loss (a)	9,978			9,027			19,956			18,054
Net periodic benefit cost	$	7,263		$	7,560		$	14,526		$	15,120

(a) Upon adoption of ASU 2017-07 on January 1, 2018, these amounts are recognized as other income (expense) in the Consolidated Statements of Income. See Note 11 for additional detail of our other income (expense).

	Other Postemployment Benefits
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2018			2017			2018			2017
	(Thousands of dollars)
Components of net periodic benefit (credit) cost
Service cost	$	589		$	627		$	1,178		$	1,254
Interest cost (a)	2,279			2,472			4,558			4,944
Expected return on assets (a)	(3,571		)	(3,147		)	(7,142		)	(6,294		)
Amortization of unrecognized prior service cost (a)	(1,142		)	(1,149		)	(2,284		)	(2,298		)
Amortization of net loss (a)	972			1,621			1,944			3,242
Net periodic benefit (credit) cost	$	(873	)	$	424		$	(1,746	)	$	848

(a) Upon adoption of ASU 2017-07 on January 1, 2018, these amounts are recognized as other income (expense) in the Consolidated Statements of Income. See Note 11 for additional detail of our other income (expense).

We recover qualified pension benefit plan and other postemployment benefit plan costs through rates charged to our customers. Certain regulatory authorities require that the recovery of these costs be based on specific guidelines. The difference between these regulatory-based amounts and the periodic benefit cost calculated pursuant to GAAP is deferred as a regulatory asset or liability and amortized to expense over periods in which this difference will be recovered in rates, as authorized by the applicable regulatory authorities. Regulatory deferrals related to net periodic benefit cost were not material for the three and six months ended June 30, 2018.

Upon adoption of ASU 2017-07 on January 1, 2018, we continue to capitalize all eligible service cost and non-service cost components under the accounting requirements of Topic 980 (Regulated Operations) for rate regulated entities. Our consolidated balance sheets reflect the capitalized non-service cost components as a regulatory asset. See Note 3 of the Notes to the Consolidated Financial Statements in this Quarterly Report for additional information.