Marcellus Share Firm Transportation Contracts - Income Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	$ 76	$ 0	$ 204	$ 0
Revenues	1,273	960	3,789	3,055
Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Sales of Purchased Oil and Gas		0		0
Purchased Oil and Gas	32	0	98	0
Revenues	945	696	2,818	2,246
Cost of Purchased of Gas | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	24	0	77	0
Firm Transportation Expense | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	7	0	18	0
Unutilized Firm Transportation Expense | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Purchased Oil and Gas	1	0	3	0
Sales of Purchased Gas, Net | Operating Segments | United States
Long-term Purchase Commitment [Line Items]
Revenues	$ (6)	$ 0	$ (17)	$ 0