Supplemental Quarterly Infomation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Quarterly Information [Abstract]
Sales and other operating revenues		$ 653,700	$ 665,600	$ 718,600	$ 749,200	$ 1,218,800	$ 1,431,000	$ 1,357,900	$ 1,281,200	$ 2,787,116	$ 5,288,933	$ 5,312,686
Income (loss) from continuing operations before income taxes		(646,500)	(2,408,000)	(110,100)	(117,700)	217,000	396,500	304,600	334,200	(3,282,262)	1,252,270	1,472,687
Income (loss) from continuing operations		(583,200)	(1,587,100)	(89,000)	3,500	442,000	271,000	142,700	169,300	(2,255,772)	1,024,973	888,137
Net income (loss)		$ (587,100)	$ (1,595,400)	$ (73,800)	$ (14,500)	$ 375,200	$ 245,700	$ 129,400	$ 155,300	$ (2,270,833)	$ 905,611	$ 1,123,473
Income (loss) from continuing operations per Common share, Basic		$ (3.39)	$ (9.22)	$ (0.51)	$ 0.02	$ 2.49	$ 1.52	$ 0.80	$ 0.94	$ (12.94)	$ 5.73	$ 4.73
Income (loss) from continuing operations per Common share, Diluted		(3.39)	(9.22)	(0.51)	0.02	2.48	1.51	0.79	0.93	(12.94)	5.69	4.69
Net income per Common share, Basic		(3.41)	(9.26)	(0.42)	(0.08)	2.11	1.38	0.72	0.86	(13.03)	5.06	5.98
Net income per Common share, Diluted		(3.41)	(9.26)	(0.42)	(0.08)	2.10	1.37	0.72	0.85	(13.03)	5.03	5.94
Cash dividend per Common share		0.35	0.35	0.35	0.35	0.35	0.35	0.3125	0.3125	1.40	1.325	$ 1.25
Market price of Common Stock, High	[1]	31.03	41.42	50.56	51.77	56.13	67.75	66.82	63.70	51.77	67.75
Market price of Common Stock, Low	[1]	$ 21.71	$ 23.76	$ 41.42	$ 43.40	$ 44.39	$ 56.18	$ 59.61	$ 55.68	$ 21.71	$ 44.39

[1] Prices are as quoted on the New York Stock Exchange.