Acquisitions, Investments and Dispositions - Mountain Valley Pipeline (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity method investment			$ 467	$ 488
Mountain Valley Pipeline | Scenario, Forecast | Minimum
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity interest		$ 3,000
Mountain Valley Pipeline | Scenario, Forecast | Maximum
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity interest		$ 3,500
CET Gas | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest acquired	12.50%		12.50%
Payments to acquire equity interest	$ 18
Equity method investment			$ 98	$ 48