| **Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) (USD $)In Millions, unless otherwise specified** | 3 Months Ended | 6 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Asset Impairment Charges [Abstract]**                                                                                                                           |           |                |   |  |   |  |   |
| Impaired of Oil and Gas Properties                                                                                                                                | $ 34           |                | $ 0 |  | $ 131 |  | $ 0 |
| Discount Rate for Impairment Model                                                                                                                                | 10.00%         |                | 10.00% |  | 10.00% |  | 10.00% |
| Quoted Prices in Active Markets (Level 1)                                                                                                                         |           |                |   |  |   |  |   |
| **Asset Impairment Charges [Abstract]**                                                                                                                           |           |                |   |  |   |  |   |
| Impaired of Oil and Gas Properties                                                                                                                                | 0              |                | 0 |  | 0 |  | 0 |
| Significant Other Observable Inputs (Level 2)                                                                                                                     |           |                |   |  |   |  |   |
| **Asset Impairment Charges [Abstract]**                                                                                                                           |           |                |   |  |   |  |   |
| Impaired of Oil and Gas Properties                                                                                                                                | 0              |                | 0 |  | 0 |  | 0 |
| Significant Unobservable Inputs (Level 3)                                                                                                                         |           |                |   |  |   |  |   |
| **Asset Impairment Charges [Abstract]**                                                                                                                           |           |                |   |  |   |  |   |
| Impaired of Oil and Gas Properties                                                                                                                                | 8              |                | 0 |  | 14 |  | 0 |
| Net Book Value                                                                                                                                                    |           |                |   |  |   |  |   |
| **Asset Impairment Charges [Abstract]**                                                                                                                           |           |                |   |  |   |  |   |
| Impaired of Oil and Gas Properties                                                                                                                                | $ 42           | [1]            | $ 0 | [1] | $ 145 | [1] | $ 0 |
|                                                                                                                                                                   |
| [1]Amount represents net book value at the date of assessment.                                                                                                    |

| X                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Risk-free interest rate assumption used in valuing an instrument.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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 Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585Reference 2: 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=28370743&loc=d3e66150-109466Reference 3: 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
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