Marcellus Shale Firm Transportation Commitments - Income Statement Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	$ 296	$ 0	$ 0
Purchased Oil and Gas | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Sales of Purchased Oil and Gas	113	0	0
Purchased Oil and Gas	108	0	0
Firm Transportation Expense | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	29	0	0
Unutilized Firm Transportation Expense | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	3	0	0
Sales of Purchased Gas, Net | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	$ 140	$ 0	$ 0