Employee and Retiree Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2015

Pension And Other Postretirement Benefits Disclosure [Line Items]

Amounts Included in Accumulated Other Comprehensive Income Not Recognized in Net Periodic Benefit Expense

(Thousands of dollars)	Pension Benefits		Other Postretirement Benefits
Net actuarial loss	$	(242,809)	(13,495)
Prior service (cost) credit		(8,903)	207
	$	(251,712)	(13,288)

Amounts Included in Accumulated Other Comprehensive Income Expected to be Amortized into Net Periodic Benefit Expense

(Thousands of dollars)	Pension Benefits		Other Postretirement Benefits
Net actuarial loss	$	(14,527)	(155)
Prior service (cost) credit		(1,295)	82
	$	(15,822)	(73)

Projected Benefit Obligations, Accumulated Benefit Obligations and Fair Value of Plan Assets for Plans where Accumulated Benefit Obligation Exceeded Fair Value of Plan Assets

	Projected Benefit Obligations			Accumulated Benefit Obligations		Fair Value of Plan Assets
(Thousands of dollars)	2015		2014	2015	2014	2015	2014
Funded qualified plans where    accumulated benefit obligation    exceeds fair value of plan assets	$	630,587	658,618	622,841	597,918	500,695	533,165
Unfunded nonqualified and directors'    plans where accumulated benefit    obligation exceeds fair value of    plan assets		148,019	147,018	140,544	127,200	–	–
Unfunded other postretirement plans		115,222	118,496	115,222	118,496	–	–

Components of Net Periodic Benefit Expense

	Pension Benefits				Other Postretirement Benefits
(Thousands of dollars)		2015	2014	2013	2015	2014	2013
Service cost	$	17,948	22,470	26,346	3,180	2,459	4,566
Interest cost		33,168	33,680	30,903	4,883	4,617	5,189
Expected return on plan assets		(34,016)	(33,723)	(28,974)	–	–	–
Amortization of prior service     cost (credit)		1,560	899	1,006	(82)	(82)	(143)
Amortization of transitional    (asset) liability		(1)	(480)	(514)	–	–	8
Recognized actuarial loss		15,147	9,471	17,338	992	5	1,484
		33,806	32,317	46,105	8,973	6,999	11,104
Termination benefits expense		8,606	–	849	–	–	–
Curtailment expense (benefit)		306	–	1,365	–	–	(442)
Net periodic benefit expense	$	42,718	32,317	48,319	8,973	6,999	10,662

Weighted-Average Assumptions used in Measurement of Benefit Obligations and Net Periodic Benefit Expense

	Benefit Obligations				Net Periodic Benefit Expense
	Pension Benefits		Other Postretirement Benefits		Pension Benefits		Other Postretirement Benefits
	December 31		December 31		Year		Year
	2015	2014	2015	2014	2015	2014	2015	2014
Discount rate	4.37%	3.94%	4.61%	4.12%	4.04%	4.56%	4.12%	4.91%
Expected return on plan assets	6.00%	6.11%	–	–	6.00%	6.11%	–	–
Rate of compensation increase	3.74%	3.69%	–	–	3.74%	3.69%	–	–

Benefit Payments Reflecting Expected Future Service as Appropriate which are Expected to be Paid in Future Years from Assets of Plans or by Company

(Thousands of dollars)	Pension Benefits		Other Postretirement Benefits
2016	$	37,255	6,251
2017		37,744	6,445
2018		38,649	6,683
2019		39,931	6,955
2020		40,903	7,246
2021-2025		222,198	40,661

One Percent Change in Assumed Health Care Cost Trend Rates

(Thousands of dollars)	1% Increase		1% Decrease
Effect on total service and interest cost components of net periodic postretirement     benefit expense for the year ended December 31, 2015	$	1,451	(1,094)
Effect on the health care component of the accumulated postretirement benefit     obligation at December 31, 2015		17,284	(13,806)

Effects of Fair Value Measurements Using Significant Unobservable Inputs on Changes in Level 3 Plan Assets

(Thousands of dollars)	Hedged Funds and Other Alternative Strategies
Total at December 31, 2013		$	32,788
Actual return on plan assets:
Relating to assets held at the reporting date			1,164
Relating to assets sold during the period			–
Purchases, sales and settlements			–
Total at December 31, 2014			33,952
Actual return on plan assets:
Relating to assets held at the reporting date			(23)
Relating to assets sold during the period			–
Purchases, sales and settlements			–
Total at December 31, 2015		$	33,929

Domestic Postretirement Plans [Member]

Pension And Other Postretirement Benefits Disclosure [Line Items]

Plans' Benefit Obligations and Fair Value of Assets and Statement of Funded Status

	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2015		2014	2015	2014
Change in benefit obligation
Obligation at January 1	$	825,552	707,254	118,496	107,001
Service cost		17,948	22,470	3,180	2,459
Interest cost		33,168	33,680	4,883	4,617
Plan amendments		8,297	–	–	–
Participant contributions		4	5	1,276	1,406
Actuarial loss (gain)		(48,019)	122,824	(7,436)	8,150
Medicare Part D subsidy		–	–	510	404
Exchange rate changes		(15,337)	(14,614)	(112)	(55)
Benefits paid		(35,936)	(35,044)	(5,575)	(5,486)
Special termination benefits		8,606	–	–	–
Curtailments		306	(11,023)	–	–
Obligation at December 31		794,589	825,552	115,222	118,496
Change in plan assets
Fair value of plan assets at January 1		560,978	533,108	–	–
Actual return on plan assets		(18,718)	31,340	–	–
Employer contributions		31,442	47,279	3,789	3,676
Participant contributions		4	5	1,276	1,406
Medicare Part D subsidy		–	–	510	404
Exchange rate changes		(14,104)	(13,284)	–	–
Benefits paid		(35,936)	(35,044)	(5,575)	(5,486)
Other		(1,984)	(2,426)	–	–
Fair value of plan assets at December 31		521,682	560,978	–	–
Funded status and amounts recognized in the     Consolidated Balance Sheets at December 31
Deferred charges and other assets		7,463	7,899	–	–
Other accrued liabilities		(7,487)	(5,996)	(5,370)	(5,515)
Deferred credits and other liabilities		(272,883)	(266,477)	(109,852)	(112,981)
Funded status and net plan liability recognized             at December 31	$	(272,907)	(264,574)	(115,222)	(118,496)

Foreign Other Postretirement Benefit Plans [Member]

Pension And Other Postretirement Benefits Disclosure [Line Items]

Plans' Benefit Obligations and Fair Value of Assets and Statement of Funded Status

	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2015		2014	2015	2014
Benefit obligation at December 31	$	197,549	222,497	643	648
Fair value of plan assets at December 31		193,933	202,305	–	–
Net plan liabilities recognized		3,616	20,192	643	648
Net periodic benefit expense		4,703	12,968	152	152

Other Postretirement Benefits [Member]

Pension And Other Postretirement Benefits Disclosure [Line Items]

Asset Allocation for Benefit Plans

At December 31, 2015, the fair value measurements of retirement plan assets within the fair value hierarchy are included in the table that follows.

			Fair Value Measurements Using
(Thousands of dollars)	Fair Value at December 31, 2015		Quoted Prices in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
Domestic Plans
Equity securities:
U.S. core equity	$	51,878	51,878	–	–
U.S. small/midcap		26,964	26,964	–	–
Hedged funds and other          alternative strategies		50,878	–	16,949	33,929
International commingled          trust fund		72,205	–	72,205	–
Emerging market commingled         equity fund		16,873	–	16,873	–
Fixed income securities:
U.S. fixed income		80,681	–	80,681	–
International commingled          trust fund		15,332	–	15,332	–
Emerging market mutual fund		6,439	–	6,439	–
Cash and equivalents		6,499	6,499	–	–
Total Domestic Plans		327,749	85,341	208,479	33,929
Foreign Plans
Equity securities funds		104,718	–	104,718	–
Fixed income securities funds		67,494	–	67,494	–
Diversified pooled fund		20,987	–	20,987	–
Cash and equivalents		734	734	–	–
Total Foreign Plans		193,933	734	193,199	–
Total	$	521,682	86,075	401,678	33,929

At December 31, 2014, the fair value measurements of retirement plan assets within the fair value hierarchy are included in the table that follows.

			Fair Value Measurements Using
(Thousands of dollars)	Fair Value at December 31, 2014		Quoted Prices in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
Domestic Plans
Equity securities:
U.S. core equity	$	67,863	67,863	–	–
U.S. small/midcap		33,709	33,709	–	–
Hedged funds and other          alternative strategies		52,905	–	18,953	33,952
International commingled          trust fund		75,702	–	75,702	–
Emerging market commingled         equity fund		19,908	–	19,908	–
Fixed income securities:
U.S. fixed income		80,577	–	80,577	–
International commingled          trust fund		17,559	–	17,559	–
Emerging market mutual fund		8,069	–	8,069	–
Cash and equivalents		2,381	2,381	–	–
Total Domestic Plans		358,673	103,953	220,768	33,952
Foreign Plans
Equity securities funds		106,694	–	106,694	–
Fixed income securities funds		66,435	–	66,435	–
Diversified pooled fund		27,813	–	27,813	–
Cash and equivalents		1,363	1,363	–	–
Total Foreign Plans		202,305	1,363	200,942	–
Total	$	560,978	105,316	421,710	33,952

Funded Defined Benefit Pension Plans [Member]

Pension And Other Postretirement Benefits Disclosure [Line Items]

Asset Allocation for Benefit Plans

	December 31,
	2015		2014
Equity securities	64.4	%	66.6	%
Fixed income securities	34.0		32.5
Cash equivalents	1.6		0.9
	100.0	%	100.0	%