Exit Costs - Transportation Commitments - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jan. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Long-term Purchase Commitment [Line Items]
Reduction of transportation contracts	$ 350
Marcellus Shale Firm Transportation Agreement
Long-term Purchase Commitment [Line Items]
Commitment amount		$ 1,000
Firm Transportation Exit Cost Accrual	$ 92	$ 92	$ 0