Supplemental Disclosures About Natural Gas, Oil and NGL Producing Activities (Cost Insurred on Natural Gas, Oil and NGL Drilling and Completion (Table) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Disclosures About Natural Gas and Oil Producing Activities [Line Items]
Costs Incurred, Acquisition of Oil and Gas Properties with Proved Reserves	$ 332	$ 48	$ 243
Costs Incurred, Acquisition of Unproved Oil and Gas Properties	2,981	4,736	6,953
Capitalized Costs, Uncompleted Wells, Equipment and Facilities	2,353	2,261	872
Capitalized Costs, Wells and Related Equipment and Facilities	6,733	5,497	4,741
Capitalized Costs Incurred in Natural Gas and Oil Drilling and Completion, Acquisitions and Divestitures	12,399	12,542	12,809
Capitalized Costs, Interest Incurred, Oil and Gas Producing Activities	976	727	711
Capitalized Costs, Asset Retirement Costs	32	3	2
Oil And Gas Benefit From Drilling Carries	$ 784	$ 2,570	$ 1,151