ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)

9 Months Ended

Sep. 30, 2017

Accumulated Other Comprehensive Income (Loss) [Line Items]

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

The following table sets forth the effect of reclassifications from accumulated other comprehensive income (loss) in our Statements of Income for the periods indicated:

	Three Months Ended						Nine Months Ended
Details about Accumulated Other Comprehensive	September 30,						September 30,						Affected Line Item in the
Income (Loss) Components	2017			2016			2017			2016			Statements of Income
	(Thousands of dollars)
Pension and other postemployment benefit plan obligations (a)
Amortization of net loss	$	10,648		$	10,040		$	31,944		$	30,113
Amortization of unrecognized prior service cost	(1,149		)	(909		)	(3,447		)	(2,725		)
	9,499			9,131			28,497			27,388
Regulatory adjustments (b)	(9,290		)	(8,943		)	(27,869		)	(26,824		)
	209			188			628			564			Income before income taxes
	(81		)	(72		)	(242		)	(217		)	Income tax expense
Total reclassifications for the period	$	128		$	116		$	386		$	347		Net income

(a) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost. See Note 8 for additional detail of our net periodic benefit cost.

(b) Regulatory adjustments represent pension and other postemployment benefit costs expected to be recovered through rates and are deferred as part of our regulatory assets. See Note 2 for additional disclosures of regulatory assets and liabilities.