Acquisitions and Divestitures (Details) bbl / d in Thousands, bbl in Thousands, $ in Millions						3 Months Ended						6 Months Ended	9 Months Ended
	Jun. 30, 2017 MMBoe	Jun. 28, 2017 USD ($) $ / MMBTU payment	Jun. 26, 2017 USD ($) a shares	May 18, 2017 USD ($) shares	Apr. 03, 2017 USD ($) bbl / d mi bbl	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($) MMcf / d MMBoe	Mar. 31, 2017 USD ($) well	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jun. 30, 2017 MMcf / d MMBoe	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) a	Jun. 27, 2017 USD ($)	Dec. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds													$ 1,028.0	$ 0.0
Loss on Marcellus Shale Upstream Divestiture						$ 4.0			$ 0.0				2,326.0	0.0
Firm transportation liability						0.0			0.0				41.0	0.0
Income (loss) before income taxes						208.0			280.0				2,483.0	1,231.0
Proved undeveloped reserves (MMBOEs) | MMBoe	(551)						(551)					(551)
Proceeds from divestiture of Onshore US													129.0	786.0
Cash consideration													616.0	0.0
Borrowings													245.0	0.0
Gain (loss) on sale						0.0			0.0				(2,270.0)	0.0
Proceeds receivable						0.0							0.0			$ 40.0
Percentage of divestiture farmed out																35.00%
Marcellus Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value		$ 1,200.0
Proceeds		1,000.0
Contingent adjustment		$ 100.0
Number of payments | payment		3
Individual payment		$ 33.3
Contingent consideration ($ per MMBtu) | $ / MMBTU		3.30
Loss on Marcellus Shale Upstream Divestiture							$ 2,300.0
Gain (loss), net of tax							$ 1,500.0
Assets															$ 3,400.0
Income (loss) before income taxes									70.0				2,300.0	237.0
Natural gas production per day (MMcf per day) | MMcf / d							393					413
CONE Gathering LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value				$ 765.0
Assets						173.0							$ 173.0
Ownership				50.00%
Ownership interest				33.50%
Onshore US
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds														20.0
Proceeds from divestiture of Onshore US						24.0
Delaware Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration								$ 301.0
Allocated to undeveloped leasehold								$ 246.0
Number of wells | well								7
Number of wells operated by company | well								4
Leaseholds and Leasehold Improvements | Marcellus Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets															$ 883.0
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
Dedications area for oil, gas and water gathering services (in acres) | a			111,000
Cash consideration			$ 245.0
Shares exchange in acquisition (shares) | shares			562,430
Proceeds from equity			$ 138.0
Borrowings			$ 90.0
Noble Midstream Partners LP | Blanco River DevCo
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional voting interests acquired in limited partnership			15.00%
Equity interest in acquiree			40.00%
Noble Midstream Partners LP | Colorado River DevCo
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional voting interests acquired in limited partnership			20.00%
Noble Midstream Partners LP | Blanco River and Colorado River DevCos
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration			$ 270.0
Noble Midstream Partners LP | Advantage Pipeline
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership					50.00%
Consideration					$ 133.0
Length of pipeline (miles) | mi					70
Shipping capacity (barrels per day) | bbl / d					150
Storage capacity (barrels per day) | bbl					490
Advantage Joint Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to acquire joint venture					$ 66.8
Maximum | Noble Midstream Partners LP | Advantage Pipeline
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Shipping capacity (barrels per day) | bbl / d					200
Member Units | CONE Gathering LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity owned (units) | shares				21,700,000
Marcellus Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed and undeveloped reserves, decreased reserves from divestiture (MMBOEs) | MMBoe	241
Decrease in proved developed reserves (MMBOEs) | MMBoe	190
Decrease in undeveloped reserves (MMBOEs) | MMBoe	51
Disposal Group, Disposed of by Sale, Not Discontinued Operations | MONTANA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds														43.0
Gain (loss) on sale														$ (23.0)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Producing and Undeveloped Net Acres in the DJ Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds						$ 5.0				$ 486.0
Purchase and sales agreement, area (acres) | a														33,100
Purchase and sales agreement, consideration									$ 505.0					$ 505.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Cyprus Block 12
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds receivable								$ 40.0
Proceeds received from farm-out agreement								$ 131.0
Percentage of divestiture farmed out								35.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Alon A And Alon C
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total transaction value											$ 73.0
Contingent adjustment											6.0
Assets											$ 67.0
Percentage of divestiture farmed out											47.00%
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Exchange | Wells Ranch Development Area
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Land exchanged (acres) | a														11,700
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Exchange | Bronco Development Area
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase and sales agreement, area (acres) | a														13,500