| **Asset Impairments (Details) (USD $)In Millions, unless otherwise specified** | 3 Months Ended | 9 Months Ended |
|--------------------------------------------------------------------------------|----------------|----------------|
||
| **Impaired Long-Lived Assets Held and Used [Line Items]**                      |           |           |   |  |   |  |
| Impairment of Oil and Gas Properties                                           | $ 0            | $ 0            | $ 73 | [1] | $ 137 | [1] |
| South Raton (Deepwater Gulf of Mexico) [Member]                                |           |           |   |  |   |  |
| **Impaired Long-Lived Assets Held and Used [Line Items]**                      |           |           |   |  |   |  |
| Impairment of Oil and Gas Properties                                           | 0              | 0              | 34 |  | 0 |  |
| Piceance (Onshore US) [Member]                                                 |           |           |   |  |   |  |
| **Impaired Long-Lived Assets Held and Used [Line Items]**                      |           |           |   |  |   |  |
| Impairment of Oil and Gas Properties                                           | 0              | 0              | 39 |  | 0 |  |
| East Texas (Onshore US) [Member]                                               |           |           |   |  |   |  |
| **Impaired Long-Lived Assets Held and Used [Line Items]**                      |           |           |   |  |   |  |
| Impairment of Oil and Gas Properties                                           | 0              | 0              | 0 |  | 116 |  |
| Other (Onshore US) [Member]                                                    |           |           |   |  |   |  |
| **Impaired Long-Lived Assets Held and Used [Line Items]**                      |           |           |   |  |   |  |
| Impairment of Oil and Gas Properties                                           | $ 0            | $ 0            | $ 0 |  | $ 21 |  |
|                                                                                |
| [1]See Note 4. Asset Impairments.                                              |

| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ImpairedLongLivedAssetsHeldAndUsedLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 27, 28, 29 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 35 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6475018&loc=d3e66150-109466Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230
+ Details**Name:**us-gaap_ImpairmentOfOilAndGasProperties**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |