Asset Impairments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge, gross	$ 1,976	$ 2,024
Asset impairment charges, net of taxes	1,353	1,308
U.S. Oil And Gas Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge, gross	1,110	1,793
Asset impairment charges, net of taxes	707	1,142
Canada Oil And Gas Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge, gross	843	163
Asset impairment charges, net of taxes	632	122
Midstream Assets [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charge, gross	23	68
Asset impairment charges, net of taxes	$ 14	$ 44