Basis of Presentation and Summary of Significant Accounting Policies (Accounts Payable and Other Current Liabliities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts Payable and Other Current Liabilities [Line Items]
Revenues and royalties due others	$ 1,337	$ 1,090
Accrued natural gas, oil and NGL drilling and production costs	525	590
Accrued acquisition costs	242	81	371
Joint interest prepayments received	749	865
Employee-related liabilibies, current	224	199
Dividends payable, current	101	99
Other	563	473
Other Liabilities, Current	$ 3,741	$ 3,397