Dispositions (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended		12 Months Ended	1 Months Ended
	Apr. 30, 2010 acre	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2010	Apr. 30, 2010 Appalachian E And P [Member]	Feb. 28, 2010 Peoples [Member]
Proceed from sale					$ 3,500,000,000	$ 542,000,000
Transaction of mineral rights in marcellus shale formation (acres)	491,000
After-tax proceeds from agreement to sell Appalachian EP	2,200,000,000
After-tax gain from agreement to sell Appalachian EP	1,400,000,000	1,400,000,000
Write-off of goodwill	134,000,000					79,000,000
Benefit recorded reflecting the reclassification of gains from AOCI to earnings in connection with the discontinuance of hedge accounting for certain cash flow hedges, before tax			42,000,000
Benefit recorded reflecting the reclassification of gains from AOCI to earnings in connection with the discontinuance of hedge accounting for certain cash flow hedges, after tax			25,000,000
Loss on sale of Peoples, after tax						140,000,000
After-tax expenses, including transaction and benefit-related costs, on the sale of Peoples						27,000,000
Income (loss) from discontinued operations, net of tax				$ 12,000,000