|**Commitments and Contingencies Commitments and Contingencies (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Commitments and Contingencies Disclosure [Abstract]**                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Minimum commitments                                                      | Minimum commitments as ofDecember 31, 2012consist of the following:Drilling, Equipment,and Purchase ObligationsTransportationand GatheringOperatingLeaseObligationsFPSOLeasePayments(1)Total(millions)2013$739$81$47$72$9392014191784272383201517586527038320161018852452862017—8748451802018 and Thereafter—311302109722Total$1,206$731$543$413$2,893(1)Annual lease payments, net to our interest, exclude regular maintenance and operational costs. SeeNote 12.  Long-Term Debt.
|                                                                        
|                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(millions)                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2013                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2014                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2015                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2016                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2017                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|2018 and Thereafter                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Total                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(1)                                                                      | Annual lease payments, net to our interest, exclude regular maintenance and operational costs. SeeNote 12.  Long-Term Debt.                                                                                                                                                                                                                                                                                                                                                         

X- Details**Name:**
                    us-gaap_CommitmentsAndContingenciesDisclosureAbstract**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    xbrli:stringItemType**Balance Type:**
                    na**Period Type:**
                    duration X- DefinitionTabular disclosure of the aggregate amount of payments due on known contractual obligations for the five years following the date of the latest balance sheet and the combined aggregate amount of maturities of known contractual obligations.+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 303 -Paragraph a -Subparagraph 5+ Details**Name:**
                    us-gaap_ContractualObligationFiscalYearMaturityScheduleTableTextBlock**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    nonnum:textBlockItemType**Balance Type:**
                    na**Period Type:**
                    duration