Basis of Presentation and Summary of Significant Accounting Policies (Assets and Liabilities Held for Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	$ 4	$ 0
Property and equipment held for sale, net	634	0
Current liabilities held for sale	21	0
Accounts Receivable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current assets held for sale	4
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	352
Oilfield Services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Property and equipment held for sale, net	27
Property, Plant and Equipment, Other Types
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Property and equipment held for sale, net	255
Accounts Payable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current liabilities held for sale	4
Accrued Liabilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups [Line Items]
Current liabilities held for sale	$ 17