Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator for Basic and Diluted Earnings per Share - [Abstract]
Net Income (Loss)	$ (284,296)		$ (4,075,739)		$ 5,268		$ (169,748)		$ 444,588		$ 1,103,618		$ 706,353		$ 660,928		$ (4,524,515)	$ 2,915,487	$ 2,197,109
Denominator for Basic Earnings per Share - [Abstract]
Weighted Average Shares (in shares)																	545,697	543,443	540,341
Potential Dilutive Common Shares -[Abstract]
Stock Options/SARs (in shares)																	0	2,526	2,316
Restricted Stock/Units and Performance Units/Stock (in shares)																	0	2,570	3,570
Denominator for Diluted Earnings per Share - [Abstract]
Adjusted Diluted Weighted Average Shares (in shares)	546,432		545,920		549,683		544,998		549,153		549,518		548,676		548,071		545,697	548,539	546,227
Net Income (Loss) Per Share [Abstract]
Basic (in dollars per share)	$ (0.52)	[1]	$ (7.47)	[1]	$ 0.01	[1]	$ (0.31)	[1]	$ 0.82	[1]	$ 2.03	[1]	$ 1.30	[1]	$ 1.22	[1]	$ (8.29)	$ 5.36	$ 4.07
Diluted (in dollars per share)	$ (0.52)	[1]	$ (7.47)	[1]	$ 0.01	[1]	$ (0.31)	[1]	$ 0.81	[1]	$ 2.01	[1]	$ 1.29	[1]	$ 1.21	[1]	$ (8.29)	$ 5.32	$ 4.02
Antidilutive Stock Options and SARs excluded from Diluted Earnings Per Share Calculation (in shares)																	10,200	700	300
Restricted Stock and Restricted Stock Units and Performance Units and Performance Stock Excluded from Calculation																	5,300

[1] The sum of quarterly net income (loss) per share may not agree with total year net income (loss) per share as each quarterly computation is based on the weighted average of common shares outstanding.