Asset Impairments (Summary of Asset Impairments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges		$ 17	$ 1,310	[1]	$ 17,647	[1]
Goodwill, impairment loss			873
Proved Oil and Gas Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges			435		16,076
Unproved Impairments [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges		217	77		260
Other Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges		$ 17	2		20
General Partner And EnLink [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill, impairment loss	$ 873		$ 873		1,328
Impairment of intangible assets					$ 223

[1] Prior year amounts have been recast due to change in accounting principle. See Note 2 in “Item 8. Financial Statements and Supplementary Data” of this report.