Exit Costs - Transportation Commitments - Rollfoward of Accrued Transportation Commitment (Details) - Marcellus Shale Firm Transportation Agreement - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jan. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Rollforward Of Contractual Obligations [Roll Forward]
Balance at Beginning of Period	$ 80	$ 80	$ 90
Firm Transportation Exit Cost Accrual	$ 92	92	0
Payments, Net of Accretion		(6)	(9)
Balance at End of Period		166	81
Other Current Liabilities
Rollforward Of Contractual Obligations [Roll Forward]
Balance at End of Period		33	12
Accrued exit costs, current				$ 13
Other Noncurrent Liabilities
Rollforward Of Contractual Obligations [Roll Forward]
Balance at End of Period		$ 133	$ 69