Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligations [Abstract]

Schedule of Reconciliation of Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligations

(Thousands of dollars)	2015		2014
Balance at beginning of year	$	875,728	880,003
Accretion expense		48,665	50,778
Liabilities incurred		76,775	70,568
Revisions of previous estimates		(85,504)	8,278
Liabilities settled		(13,359)	(36,818)
Liabilities assumed by purchaser of oil and gas assets		(33,448)	(69,416)
Changes due to translation of foreign currencies		(43,545)	(27,665)
Balance at end of year		825,312	875,728
Current portion of liability at end of year*		(31,838)	(34,202)
Noncurrent portion of liability at end of year	$	793,474	841,526

*Included in Other Accrued Liabilities on the Consolidated Balance Sheet.