Net Gains on Sales of Fixed Assets Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Property Plant Equipment	$ 132	$ (7)	$ 290	$ (5)
Sale to MarkWest Oklahoma Gas Company L.L.C. [Member]
Significant Acquisitions and Disposals [Line Items]
Proceeds from Sale of Property, Plant, and Equipment			252
Gas Gathering and Processing Equipment [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Property Plant Equipment	132	7	311	8
Gas Gathering and Processing Equipment [Member] | Sale to SemGas, L.P. [Member]
Significant Acquisitions and Disposals [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	306
Gain (Loss) on Sale of Property Plant Equipment			141
Gas Gathering and Processing Equipment [Member] | Sale to MarkWest Oklahoma Gas Company L.L.C. [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Property Plant Equipment			105
Gas Gathering and Processing Equipment [Member] | Sale to Western Gas Partners, LP [Member]
Significant Acquisitions and Disposals [Line Items]
Proceeds from Sale of Property, Plant, and Equipment			134
Gain (Loss) on Sale of Property Plant Equipment			$ 55