Acquisitions, Divestitures, and Assets Held for Sale - Divestitures and Assets Held for Sale (Detail) - USD ($) $ in Millions			2 Months Ended	12 Months Ended
		Mar. 17, 2017	Feb. 16, 2018	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				$ 4,008		$ 2,356	$ 1,415
Gains (losses) on divestitures, net	[1]			674	[2]	(757)	(1,022)
Amount of goodwill written off allocated to divestitures				209		397	184
Assets Held for Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term assets associated with assets held for sale				573		1,200
Long-term liabilities associated with assets held for sale				27		66
Goodwill associated with assets held for sale						193
Certain Alaska Assets [Member] | Assets Held for Sale [Member] | Subsequent Event [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments			$ 383
Exploration and Production Reporting Segment [Member] | Certain South Texas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				2,100
Gain (loss) on divestitures				(729)
Exploration and Production Reporting Segment [Member] | Certain Southeast Texas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				533
Gain (loss) on divestitures				(282)
Exploration and Production Reporting Segment [Member] | Certain Moxa Wyoming Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				313
Gain (loss) on divestitures				204
Exploration and Production Reporting Segment [Member] | Certain Alaska Assets [Member] | Assets Held for Sale [Member] | Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member] | Nonrecurring [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Losses on assets held for sale				154
Exploration and Production Reporting Segment [Member] | Certain Wyoming Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments						588
Gain (loss) on divestitures						58
Exploration and Production Reporting Segment [Member] | Certain Elm Grove East Texas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments						89
Gain (loss) on divestitures						64
Exploration and Production Reporting Segment [Member] | Certain EOR Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments							675
Gain (loss) on divestitures							350
Exploration And Production And WES Midstream Reporting Segment [Member] | Certain Utah Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				69
Gain (loss) on divestitures				52
Exploration And Production And WES Midstream Reporting Segment [Member] | Certain Kansas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments						159
Gain (loss) on divestitures						4
Exploration And Production And WES Midstream Reporting Segment [Member] | Certain Freestone And Dew Pinnacle East Texas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments							425
Gain (loss) on divestitures							110
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain Marcellus Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments				951
Gain (loss) on divestitures				$ 55
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain Marcellus Assets [Member] | Assets Disposed of by Sale [Member] | Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member] | Nonrecurring [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Losses on assets held for sale						129
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain West Texas Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments						221
Gain (loss) on divestitures						52
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain East Chalk and Carthage East Texas/Louisiana Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments						1,000
Gain (loss) on divestitures						$ 439
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain Coalbed Methane Assets [Member] | Assets Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds received, net of closing adjustments							154
Gain (loss) on divestitures							$ 538
Western Gas Partners, LP [Member] | Delaware Basin Joint Venture System [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on property exchange		$ 126

[1] Includes goodwill allocated to divestitures of $209 million in 2017, $397 million in 2016, and $184 million in 2015.

[2] Includes the $126 million gain related to the property exchange discussed above.