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Additional Shareholders' Equity Information - Common Stock Rollforward (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Apr. 24, 2017	Dec. 31, 2018	Dec. 31, 2017	Feb. 15, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares Received In Payment of Withholding Taxes Due on Vesting of Shares of Restricted Stock		720,000
Incremental Shares From Assumed Conversion of Dilutive Stock Options, Restricted Stock, and Shares of Common Stock in Rabbi Trust		0	0
Number of Antidilutive Stock Options, Shares of Restricted Stock and Shares of Common Stock in Rabbi Trust excluded from Dilutive Earnings (Loss) per Share (4)		15,004,591	15,619,276
Share repurchase program authorized amount				$ 750
Repurchase price (in usd per share)		$ 29.49
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance		528,743,381	471,360,427
Exercise of Common Stock Options		576,617	382,882
Restricted stock awards, net of forfeitures		2,488,363	2,912,936
Purchase and Retirement of Common Stock		(10,008,128)	0
Shares Exchanged in Clayton Williams Energy Acquisition		(745,232)	54,087,136
Shares, ending balance		521,055,001	528,743,381
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, beginning balance		38,786,969	37,961,316
Shares Received In Payment of Withholding Taxes Due on Vesting of Shares of Restricted Stock		267,258	1,026,891
Rabbi Trust Shares Distributed and/or Sold		(202,239)	(201,238)
Shares, ending balance		38,851,988	38,786,969
Clayton Williams Energy
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares Exchanged in Clayton Williams Energy Acquisition	56,000,000
Restricted Stock \| Clayton Williams Energy
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Awarded shares		1,900,000