Dispositions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from asset sales			$ 607	$ 783
Gain (loss) on asset sales, pre-tax	$ 14	$ 274	$ 32	$ 276
Utica Shale Play, Eastern Ohio
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from asset sales	396
Gain (loss) on asset sales, pre-tax	14
Gain (loss) on asset sales, after-tax	$ 14
Permian Basin
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from asset sales		597
Gain (loss) on asset sales, pre-tax		273
Gain (loss) on asset sales, after-tax		280
Exploration and Production | Permian Basin
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on asset sales, after-tax		314
Midstream | Permian Basin
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on asset sales, after-tax		$ (34)