Dispositions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on asset sales, pre-tax	$ 0		$ 14	$ 22	$ 32
Proceeds from asset sales				22	607
Utica Shale Play
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on asset sales, pre-tax		$ 22	14	22	14
Gain (loss) on asset sale, after-tax		$ 22	14	$ 22	14
Proceeds from asset sales			$ 396		$ 396