Dispositions (Narrative) (Details) (USD $)	12 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2012	Apr. 30, 2010 Appalachian E & P acre	Jun. 30, 2010 Appalachian E & P	Feb. 28, 2010 Peoples	Dec. 31, 2010 Peoples	Mar. 31, 2010 Operating Revenue Appalachian E & P
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
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
Write-off of goodwill	11,000,000		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