Business Segments (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Total Assets	$ 10,229,214		$ 10,229,214		$ 10,304,940
External Revenues	1,303,425	$ 630,700	2,957,443	$ 1,560,328
Income (Loss)	574,076	137,309	918,094	(156,555)
Continuing operations
Segment Reporting Information [Line Items]
Total Assets	10,228,400		10,228,400
External Revenues	1,303,400	630,700	2,957,400	1,560,300
Income (Loss)	574,500	138,000	920,000	(156,000)
Discontinued operations, net of tax
Segment Reporting Information [Line Items]
Total Assets	800		800
External Revenues	0	0	0	0
Income (Loss)	(400)	(700)	(1,900)	(600)
Corporate
Segment Reporting Information [Line Items]
Total Assets	1,014,000		1,014,000
External Revenues	115,200	(59,100)	(302,600)	(493,300)
Income (Loss)	57,400	(98,800)	(363,700)	(577,600)
Exploration and production | Operating Segments
Segment Reporting Information [Line Items]
Total Assets	9,214,400		9,214,400
External Revenues	1,188,200	689,800	3,260,000	2,053,600
Income (Loss)	517,100	236,800	1,283,700	421,600
Exploration and production | Operating Segments | United States
Segment Reporting Information [Line Items]
Total Assets	6,901,000		6,901,000
External Revenues	973,800	565,200	2,659,200	1,704,400
Income (Loss)	481,500	168,100	1,225,900	481,800
Exploration and production | Operating Segments | Canada
Segment Reporting Information [Line Items]
Total Assets	2,076,000		2,076,000
External Revenues	209,600	124,600	582,300	349,200
Income (Loss)	41,400	73,900	111,300	(37,700)
Exploration and production | Operating Segments | Other
Segment Reporting Information [Line Items]
Total Assets	237,400		237,400
External Revenues	4,800	0	18,500	0
Income (Loss)	$ (5,800)	$ (5,200)	$ (53,500)	$ (22,500)