Divestitures (Narrative) (Details) - USD ($)	3 Months Ended					9 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Business Acquisition [Line Items]
Gain on sale of aggregate ownership interest, before-tax			$ 2,607,000,000		$ (1,000,000)	$ 2,607,000,000	$ (1,000,000)
Divestitures of property and equipment							400,000,000
Gain recognized			6,000,000		$ 170,000,000	(5,000,000)	$ 200,000,000
Barnett Shale [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment				$ 553,000,000
Percentage of proved reserves associated with divestiture assets compared to total estimated proved reserves				10.00%
Divestitures of property and equipment net of purchase price adjustments				$ 481,000,000
Gain recognized				0
Settlement expenses relating to gas processing contracts				$ 40,000,000
Scenario, Forecast [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment	$ 100,000,000
Scenario, Forecast [Member] | Delaware Basin and Barnett Shale [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment		$ 320,000,000
Maximum [Member]
Business Acquisition [Line Items]
Percentage of proved reserves associated with divestiture assets compared to total estimated proved reserves							1.00%
EnLink and General Partner [Member]
Business Acquisition [Line Items]
Proceeds from sale of aggregate ownership interest			3,125,000,000
Gain on sale of aggregate ownership interest, after-tax			2,200,000,000
Gain on sale of aggregate ownership interest, before-tax			2,600,000,000
Share Repurchase Program [Member] | Maximum [Member]
Business Acquisition [Line Items]
Share repurchase program, maximum authorized amount			$ 4,000,000,000.0			$ 4,000,000,000.0		$ 1,000,000,000.0