EMPLOYEE BENEFIT PLANS (Tables)

12 Months Ended

Dec. 31, 2016

Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]

Schedule of Assumptions Used [Table Text Block]

Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postemployment benefits for the periods indicated:



	December 31,
	2016	2015
Discount rate - pension plans	4.30%	4.75%
Discount rate - other postemployment plans	4.20%	4.75%
Compensation increase rate	3.25% - 3.40%	3.35% - 3.40%

The following table sets forth the weighted-average assumptions used by us to determine the periodic benefit costs for the periods indicated:



	Nine Months Ended September 30,	Three Months Ended December 31,	Years Ended December 31,
	2016	2016	2015		2014
Discount rate - pension plans	4.75%	4.75%	4.25%/4.75%	(a)	5.25%
Discount rate - other postemployment plans	4.75%	3.75%	4.25%/4.75%	(a)	5.00%
Expected long-term return on plan assets - pension plans	7.75%	7.75%	7.75%		7.75%
Expected long-term return on plan assets - other postemployment plans	8.00%	7.75%	7.75%		7.75%
Compensation increase rate	3.35% - 3.40%	3.35% - 3.40%	3.30% - 3.50%		3.35% - 3.50%

Schedule of Defined Benefit Plans Disclosures [Table Text Block]

The following table sets forth our defined benefit pension and other postemployment benefit plans, benefit obligations and fair value of plan assets for the periods indicated:



	Pension Benefits						Other Postemployment Benefits
	December 31,						December 31,
	2016			2015			2016			2015
Changes in Benefit Obligation	(Thousands of dollars)
Benefit obligation, beginning of period	$	985,624		$	1,028,171		$	228,253		$	257,688
Service cost	12,055			13,660			2,675			3,257
Interest cost	45,550			43,542			10,235			10,628
Plan participants’ contributions	—			—			3,043			2,915
Actuarial loss (gain)	25,886			(47,607		)	14,309			(19,702		)
Benefits paid	(71,066		)	(52,142		)	(15,450		)	(14,632		)
Plan amendment	—			—			483			(11,901		)
Settlements	(31,518		)	—			—			—
Benefit obligation, end of period	966,531			985,624			243,548			228,253

Change in Plan Assets
Fair value of plan assets, beginning of period	785,161			845,396			155,495			151,777
Actual return on plan assets	48,768			(9,026		)	9,733			1,335
Employer contributions	12,441			933			13,225			14,100
Plan participants’ contributions	—			—			3,043			2,915
Benefits paid	(71,066		)	(52,142		)	(15,450		)	(14,632		)
Settlements	(35,718		)	—			—			—
Fair value of assets, end of period	739,586			785,161			166,046			155,495
Balance at December 31	$	(226,945	)	$	(200,463	)	$	(77,502	)	$	(72,758	)

Current liabilities	$	(941	)	$	(912	)	$	—		$	—
Noncurrent liabilities	(226,004		)	(199,551		)	(77,502		)	(72,758		)
Balance at December 31	$	(226,945	)	$	(200,463	)	$	(77,502	)	$	(72,758	)

Schedule of Net Benefit Costs [Table Text Block]

Components of Net Periodic Benefit Cost - The following tables set forth the components of net periodic benefit cost for our defined benefit pension and other postemployment benefit plans for the period indicated:



	Pension Benefits
	Year Ended December 31,
	2016			2015			2014
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	12,055		$	13,660		$	11,620
Interest cost	45,550			43,542			43,791
Expected return on assets	(61,183		)	(61,769		)	(59,862		)
Amortization of unrecognized prior service cost	—			266			549
Amortization of net loss	35,543			42,226			30,200
Settlements	—			27			773
Net periodic benefit cost	$	31,965		$	37,952		$	27,071



	Other Postemployment Benefits
	Year Ended December 31,
	2016			2015			2014
	(Thousands of dollars)
Components of net periodic benefit cost
Service cost	$	2,675		$	3,257		$	3,468
Interest cost	10,235			10,628			11,605
Expected return on assets	(12,370		)	(11,892		)	(11,393		)
Amortization of unrecognized prior service cost	(3,316		)	(2,228		)	(1,760		)
Amortization of net loss	5,369			5,268			3,969
Net periodic benefit cost	$	2,593		$	5,033		$	5,889

Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]

Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss) related to our defined benefit pension benefits for the period indicated:



	Pension Benefits
	Year Ended December 31,
	2016			2015			2014
	(Thousands of dollars)
Net gain (loss) arising during the period	$	(1,262	)	$	339		$	(3,543	)
Amortization of loss	751			917			518
Deferred income taxes	197			(483		)	1,244
Total recognized in other comprehensive income (loss)	$	(314	)	$	773		$	(1,781	)

Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]

The tables below set forth the amounts in accumulated other comprehensive income (loss) that had not yet been recognized as components of net periodic benefit expense for the periods indicated:



	Pension Benefits
	December 31,
	2016			2015
	(Thousands of dollars)
Prior service credit (cost)	$	—		$	—
Accumulated loss	(414,757		)	(407,798		)
Accumulated other comprehensive loss before regulatory assets	(414,757		)	(407,798		)
Regulatory asset for regulated entities	407,073			400,625
Accumulated other comprehensive loss after regulatory assets	(7,684		)	(7,173		)
Deferred income taxes	2,969			2,772
Accumulated other comprehensive loss, net of tax	$	(4,715	)	$	(4,401	)



	Other Postemployment Benefits
	December 31,
	2016			2015
	(Thousands of dollars)
Prior service credit (cost)	$	10,211		$	14,010
Accumulated loss	(62,084		)	(50,447		)
Accumulated other comprehensive loss before regulatory assets	(51,873		)	(36,437		)
Regulatory asset for regulated entities	51,873			36,437
Accumulated other comprehensive loss after regulatory assets	—			—
Deferred income taxes	—			—
Accumulated other comprehensive loss, net of tax	$	—		$	—

Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]

The following table sets forth the amounts recognized in either accumulated comprehensive income (loss) or regulatory assets expected to be recognized as components of net periodic benefit expense in the next fiscal year:



	Pension Benefits		Other Postemployment Benefits
Amounts to be recognized in 2017	(Thousands of dollars)
Prior service credit (cost)	$	—	$	(4,597	)
Actuarial net loss	$	36,107	$	6,484

Schedule of Health Care Cost Trend Rates [Table Text Block]

Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated:



	2016	2015
Health care cost-trend rate assumed for next year	7.25%	4.00% - 7.50%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)	5.00%	4.00% - 5.00%
Year that the rate reaches the ultimate trend rate	2022	2022

Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]

Assumed health care cost-trend rates have a significant effect on the amounts reported for our health care plans. A one percentage point change in assumed health care cost-trend rates would have the following effects:



	One Percentage		One Percentage
	Point Increase		Point Decrease
	(Thousands of dollars)
Effect on total of service and interest cost	$	233	$	(232	)
Effect on other postemployment benefit obligation	$	3,937	$	(3,991	)

Schedule of Allocation of Plan Assets [Table Text Block]

Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. To achieve this strategy, we have established a liability-driven investment strategy to change the allocations as the plan reaches certain funded status. The plan’s investments include a diverse blend of various domestic and international equities, investment-grade debt securities which mirror the cash flows of our liability, insurance contracts and alternative investments. The current target allocation for the assets of our defined benefit pension plan is as follows:




U.S. large-cap equities	37.4	%
Investment-grade bonds	30.0	%
Developed foreign large-cap equities	10.6	%
Alternative investments	7.7	%
Mid-cap equities	5.6	%
Emerging markets equities	5.0	%
Small-cap equities	3.7	%
Total	100	%

As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock.

The current target allocation for the assets of our other postemployment benefits plan is 30 percent fixed income securities and 70 percent equity securities.

The following tables set forth our pension benefits and other postemployment benefits plan assets by fair value category as of the measurement date:



	Pension Benefits
	December 31, 2016
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	371,655	$	58,987	$	—	$	430,642
Government obligations	—		47,445		—		47,445
Corporate obligations (b)	—		129,036		—		129,036
Cash and money market funds (c)	13,786		16,114		—		29,900
Insurance contracts and group annuity contracts	—		—		45,140		45,140
Other investments (d)	—		71		57,352		57,423
Total assets	$	385,441	$	251,653	$	102,492	$	739,586

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(d) - This category represents alternative investments such as hedge funds and other financial instruments.



	Pension Benefits
	December 31, 2015
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	405,935	$	62,150	$	—	$	468,085
Government obligations	—		44,651		—		44,651
Corporate obligations (b)	—		139,396		—		139,396
Cash and money market funds (c)	5,429		10,279		—		15,708
Insurance contracts and group annuity contracts	—		—		56,465		56,465
Other investments (d)	2,884		—		57,972		60,856
Total assets	$	414,248	$	256,476	$	114,437	$	785,161

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(d) - This category represents alternative investments such as hedge funds and other financial instruments.



	Other Postemployment Benefits
	December 31, 2016
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	39,817	$	7,323	$	—	$	47,140
Government obligations	—		75		—		75
Corporate obligations (b)	—		19,948		—		19,948
Cash and money market funds (c)	74		16,989		—		17,063
Insurance contracts and group annuity contracts	—		81,820		—		81,820
Total assets	$	39,891	$	126,155	$	—	$	166,046

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.



	Other Postemployment Benefits
	December 31, 2015
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	54,560	$	7,498	$	—	$	62,058
Government obligations	—		64		—		64
Corporate obligations (b)	—		200		—		200
Cash and money market funds (c)	233		13,322		—		13,555
Insurance contracts and group annuity contracts	—		79,531		—		79,531
Other investments (d)	4		—		83		87
Total assets	$	54,797	$	100,615	$	83	$	155,495

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(d) - This category represents alternative investments such as hedge funds.

Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]

The following table sets forth the reconciliation of Level 3 fair value measurements of our pension plans for the periods indicated:



	Pension Benefits
	Insurance Contracts			Other Investments			Total
	(Thousands of dollars)
January 1, 2015	$	59,877		$	57,914		$	117,791
Net realized and unrealized gains (losses)	2,188			58			2,246
Settlements	(5,600		)	—			(5,600		)
December 31, 2015	$	56,465		$	57,972		$	114,437
Net realized and unrealized gains (losses)	4,518			(620		)	3,898
Sales and settlements	(15,843		)	—			(15,843		)
December 31, 2016	$	45,140		$	57,352		$	102,492

Schedule of Expected Benefit Payments [Table Text Block]

The following table sets forth the pension benefits and other postemployment benefits payments expected to be paid in 2017-2026:



	Pension Benefits		Other Postemployment Benefits
Benefits to be paid in:	(Thousands of dollars)
2017	$	51,539	$	16,165
2018	$	52,660	$	16,815
2019	$	53,450	$	17,073
2020	$	54,812	$	17,379
2021	$	56,033	$	17,401
2022 through 2026	$	294,519	$	86,559