Acquisitions and Divestitures - Consideration Transferred and Purchase Price Allocation (Details) - USD ($) $ in Millions		6 Months Ended
	Apr. 24, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Fair Value of Common Stock Issued	$ 1,851
Plus: Cash Consideration Paid to Clayton Williams Energy Stockholders	637	$ 0	$ 616
Total Purchase Price	2,488
Plus Liabilities Assumed by Noble Energy:
Accounts Payable	99
Other Current Liabilities	38
Long-Term Deferred Tax Liability	515
Long-Term Debt	595
Asset Retirement Obligations	63
Total Purchase Price Plus Liabilities Assumed	3,798
Cash and Cash Equivalents	21
Other Current Assets	70
Oil and Gas Properties:
Proved Reserves	722
Undeveloped Leasehold Costs	1,571
Gathering and Processing Assets	48
Asset Retirement Costs	63
Other Noncurrent Assets	12
Goodwill	1,291	$ 1,402		$ 1,310
Total Asset Value	$ 3,798