Summary of Assets and Liabilities Held for Sale (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	$ 111	$ 0
Property and equipment held for sale, net	2,307	0
Long-term assets held for sale	123
Current liabilities held for sale	176
Long-term liabilities held for sale	2	0
Cash
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	14
Accounts Receivable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	90
Other Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	7
Natural gas gathering systems and treating plants, net of accumulated depreciation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Property and equipment held for sale, net	2,027
Oilfield services equipment, net of accumulated depreciation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Property and equipment held for sale, net	24
Other property and equipment, net of accumulated depreciation and amortization
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Property and equipment held for sale, net	256
Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Long-term assets held for sale	123
Accounts Payable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current liabilities held for sale	33
Accrued Liabilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current liabilities held for sale	143
Asset Retirement Obligation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Long-term liabilities held for sale	$ 2