EMPLOYEE BENEFIT PLANS (Tables)

3 Months Ended

Mar. 31, 2019

Employee Benefit Plans [Line Items]

Schedule of Net Benefit Costs [Table Text Block]

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
	March 31,
	2019			2018
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	3,008		$	3,230
Interest cost (a)	10,168			9,200
Expected return on assets (a)	(15,485		)	(15,145		)
Amortization of net loss (a)	8,260			9,978
Net periodic benefit cost	$	5,951		$	7,263

(a) These amounts, net of any amounts capitalized as a regulatory asset since adoption of ASU 2017-07 on January 1, 2018, have been recognized as other income (expense), net in the consolidated statements of income. See Note 12 for additional detail of our other income (expense).

	Other Postemployment Benefits
	Three Months Ended
	March 31,
	2019			2018
	(Thousands of dollars)
Components of net periodic benefit cost (credit)
Service cost	$	434		$	589
Interest cost (a)	2,329			2,279
Expected return on assets (a)	(3,147		)	(3,571		)
Amortization of unrecognized prior service credit (a)	(168		)	(1,142		)
Amortization of net loss (a)	561			972
Net periodic benefit cost (credit)	$	9		$	(873	)

(a) These amounts, net of any amounts capitalized as a regulatory asset since adoption of ASU 2017-07 on January 1, 2018, have been recognized as other income (expense), net in the consolidated statements of income. See Note 12 for additional detail of our other income (expense).