Exit Cost - Transportation Commitments - Rollforward of Accrued Transportation Commitment (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Rollforward Of Contractual Obligations [Roll Forward]
Long-term Portion Included in Other Noncurrent Liabilities		$ 129	$ 67
Marcellus Shale Firm Transportation Obligations
Rollforward Of Contractual Obligations [Roll Forward]
Balance at Beginning of Period	$ 80	80	90
Exit Cost Accrual	92	88	0
Payments, Net of Accretion		(5)	(10)
Balance at End of Period		163	80
Less Current Portion Included in Other Current Liabilities		34	13
Long-term Portion Included in Other Noncurrent Liabilities		$ 129	$ 67
Long term purchase offset gain	$ 4