Basis of Presentation - Balance Sheet Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable, Net
Commodity Sales	$ 413		$ 455
Joint Interest Billings	234		207
Other	77		103
Allowance for Doubtful Accounts	(17)		(17)
Total	707		748
Other Current Assets
Inventories, Materials and Supplies	43		66
Inventories, Crude Oil	17		16
Assets Held for Sale	751		629
Restricted Cash	30	$ 0	38	$ 30
Prepaid Expenses and Other Current Assets (3)	54		31
Total	895		780
Other Noncurrent Assets
Equity Method Investments	378		305
Customer-Related Intangible Assets	334		0
Investment in Tamar Petroleum Ltd	162		0
Mutual Fund Investments	56		57
Net Deferred Income Tax Asset	25		25
Other Assets, Noncurrent	66		74
Total	1,021		461
Other Current Liabilities
Production and Ad Valorem Taxes	93		84
Commodity Derivative Liabilities	112		58
Income Taxes Payable	32		18
Asset Retirement Obligations	51		51
Interest Payable	94		67
Current Portion of Capital Lease Obligations	54		61
Liabilities Associated with Assets Held for Sale	231		55
Other Liabilities, Current	124		184
Total	791		578
Other Noncurrent Liabilities
Deferred Compensation Liabilities	180		197
Asset Retirement Obligations	577		824
Marcellus Shale Firm Transportation Commitment	73		76
Production and Ad Valorem Taxes	86		69
Other Liabilities, Noncurrent	97		79
Total	1,013		$ 1,245
Tamar and Dalit Fields
Other Current Assets
Prepaid Expenses and Other Current Assets (3)	14
Other Noncurrent Liabilities
Ownership Interest, Percentage			7.50%
Other Current Liabilities
Other Noncurrent Liabilities
Firm transportation liability	11	$ 14
CNX Midstream Partners
Other Noncurrent Assets
Equity Method Investments	$ 72