Cash Flow Disclosures (Tables)

6 Months Ended

Jun. 30, 2016

Cash Flow Disclosures [Abstract]

Cash Flow Activities

	Six Months Ended June 30
(Thousands of dollars)	2016		2015
Net (increase) decrease in operating working capital other than    cash and cash equivalents:
Decrease in accounts receivable	$	109,105	284,542
Increase in inventories		(4,659)	(25,547)
Decrease (increase) in prepaid expenses		99,524	(40,191)
Decrease in deferred income tax assets		5,564	5,092
Decrease in accounts payable and accrued liabilities		(337,302)	(84,781)
Increase (decrease) in current income tax liabilities		40,975	(31,944)
Net (increase) decrease in noncash operating working capital	$	(86,793)	107,171
Supplementary disclosures:
Cash income taxes paid (refunded), net	$	(4,367)	90,419
Interest paid, net of amounts capitalized		52,654	55,658
Non-cash investing activities:
Asset retirement costs capitalized	$	8,693	6,703
Decrease in capital expenditure accrual		165,329	336,952