Acquisitions and Divestitures - Narrative (Details) $ in Millions											1 Months Ended		3 Months Ended				9 Months Ended
	Oct. 03, 2018 shares	Oct. 03, 2018 USD ($)	Oct. 02, 2018 shares	Mar. 14, 2018 USD ($) shares	Feb. 15, 2018 USD ($) $ / bbl	Jan. 31, 2018 USD ($)	Jun. 28, 2017 USD ($) $ / MMBTU	Jun. 26, 2017 USD ($) a shares	Apr. 24, 2017 USD ($) shares	Apr. 03, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Jan. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($) shares	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($) MMcf / d MMBoe well	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($) MMBoe well	Apr. 11, 2018 MMBoe	Feb. 01, 2018 shares	Jan. 29, 2018	Jan. 28, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2017 Bcf	Dec. 31, 2017 MMBoe	Dec. 31, 2017 shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset Impairments													$ 0.0			$ 0.0	$ 168.0	$ 0.0
Proceeds from divestiture																	182.0	129.0
Gain (loss) on divestiture													$ 193.0			$ 0.0	859.0	0.0
Proceeds from Sale of 7.5% Interest in Tamar Field																	484.0	0.0
Proceeds from sale																	$ 691.0	0.0
Equity owned (units) | shares											0		0				0									21,692,198
Consideration									$ 2,488.0
Cash consideration									637.0								$ 0.0	616.0
Intangible assets											$ 318.0		$ 318.0				318.0						$ 0.0
Goodwill									1,291.0		$ 1,401.0		1,401.0				1,401.0						$ 1,310.0
Undeveloped Leasehold Costs									1,571.0
Fair value of common stock issued									1,851.0
Long-Term Debt									595.0
Gain (loss) on disposition																	$ 0.0	(2,326.0)
Natural gas production per day | MMcf / d																393
CONE Gathering LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture												$ 308.0	248.0	$ 135.0
Gain (loss) on divestiture												$ 196.0	$ 198.0	$ 109.0
Shares sold (in shares) | shares													14,200,000	7,500,000
Ownership						50.00%					22.30%	50.00%	22.30%				22.30%			34.10%
Greeley Crescent Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture											$ 64.0
Gain (loss) on divestiture											0.0
Marcellus Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value							$ 1,200.0
Proceeds from Divestitures							1,000.0										$ 0.0	$ 1,028.0
Adjustment to consideration							100.0
Adjustment to consideration, individual payment amounts							$ 33.3
Minimum index price for contingent payments to be required (in usd per unit) | $ / MMBTU							3.30
Gain (loss) on disposition																$ 2,300.0
Gain (loss) on sale																1,500.0
Assets							$ 3,400.0
Exit costs																$ 41.0
Period increase (decrease) | MMBoe																241
Proved developed reserves | MMBoe																190		190
Proved undeveloped reserves | MMBoe																51		51
Saddle Butte
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration						$ 681.0
Cash consideration						663.0
Liabilities assumed						18.0						$ 18.0
Property, plant and equipment											206.0		$ 206.0				206.0
Intangible assets											340.0		340.0				340.0
Goodwill											$ 110.0		$ 110.0				$ 110.0
Clayton Williams Energy
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration									2,500.0
Cash consideration									637.0
Goodwill									$ 1,300.0
Shares exchange in acquisition (shares) | shares									56,000,000
Fair value of common stock issued									$ 1,900.0
Long-Term Debt																$ 595.0		$ 595.0
Bolt-on acquisition in the Delaware Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to acquire oil and gas properties																		301.0
Undeveloped Leasehold Costs																$ 246.0		$ 246.0
Productive oil wells | well																7		7
Number of productive wells | well																4		4
Noble Midstream Partners LP | Blanco River DevCo
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage acquired								15.00%
Step acquisition, percentage acquired								40.00%
Noble Midstream Partners LP | Colorado River DevCo
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration								$ 270.0
Percentage acquired								20.00%
Tamar and Dalit Fields
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest																					25.00%	32.50%
CNX Midstream Partners
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity owned (units) | shares																				21,700,000
Advantage Joint Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to acquire interest										$ 66.5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Tamar and Dalit Fields
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on divestiture				$ 376.0
Estimated capacity																								502	84
Percentage ownership sold				7.50%							7.50%		7.50%				7.50%
Shares received in divestiture (in shares) | shares				38,500,000
Value of shares issued				$ 224.0
Gain attributable to change in fair value				$ 190.0
Discount percent				15.00%
Loss from change in fair value													$ 15.0				$ 25.0
Tax effect				$ 86.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southwest Royalties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale												$ 60.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Other Divestitures
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value											$ 58.0		58.0				58.0
Gain (loss) on divestiture																	4.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf of Mexico Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value					$ 480.0
Asset Impairments															$ 168.0		$ 168.0
Proceeds from divestiture													383.0
Gain (loss) on divestiture													$ (24.0)
Contingent consideration					$ 100.0
Contingent consideration basis, price per barrel (in usd per barrel) | $ / bbl					2
Price benchmark (in usd per barrel) | $ / bbl					63
Estimated capacity | MMBoe																			23
Greenfield Midstream | Saddle Butte
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration						$ 343.0
Leaseholds and Leasehold Improvements | Marcellus Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets							$ 883.0
Corporate Joint Venture | Advantage Pipeline
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership										5000.00%
Consideration										$ 133.0
Subsidiaries | Blanco River And Colorado River DevCos
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration								$ 270.0
Cash consideration								$ 245.0
Shares exchange in acquisition (shares) | shares								562,430
Gas and oil area developed | a								111,000
Proceeds from issuance								$ 138.0
Proceeds from Noble Midstream Services Revolving Credit Facility								$ 90.0
Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Tamar and Dalit Fields
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Shares sold (in shares) | shares	16,600,000		21,900,000
Pre-tax proceeds from sale		$ 163.0