Asset Impairments (Components of Asset Impairments) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges	$ 100	$ 300	$ 1,500	$ 3,000	$ 5,300	$ 5,900	$ 4,200	$ 5,500	$ 4,975	$ 20,820	$ 1,953
Goodwill, impairment loss									873	1,328
U.S. Oil And Gas Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges									2,809	17,992
Canada Oil And Gas Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges									1,291	1,257
Other Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges									2	20	12
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
Canada [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill, impairment loss											$ 1,941