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, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity method investment			$ 488	$ 574
Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest acquired	12.50%
Payments to acquire equity interest	$ 18
Equity method investment			$ 48
Mountain Valley Pipeline | Gas | Minimum | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity interest		$ 3,000
Mountain Valley Pipeline | Gas | Maximum | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity interest		$ 3,500