| **Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Aging of Exploratory Well Costs (Details) - USD ($) $ in Millions** | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 |
|--------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | $ 510         | $ 699         | $ 1,258       |
| Ownership interest sold                                                                                                                    | 35.00%        | 35.00%        |          |
| Suspended Since 2015 and 2016                                                                                                              |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | $ 81          |          |          |
| Suspended Since 2013 and 2014                                                                                                              |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 203           |          |          |
| Suspended Since 2012 and Prior                                                                                                             |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 226           |          |          |
| Katmai                                                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 147           |          |          |
| Katmai | Suspended Since 2015 and 2016                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 56            |          |          |
| Katmai | Suspended Since 2013 and 2014                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 91            |          |          |
| Katmai | Suspended Since 2012 and Prior                                                                                                    |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 0             |          |          |
| Felicita (Block O)                                                                                                                         |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 47            |          |          |
| Felicita (Block O) | Suspended Since 2015 and 2016                                                                                         |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 3             |          |          |
| Felicita (Block O) | Suspended Since 2013 and 2014                                                                                         |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 12            |          |          |
| Felicita (Block O) | Suspended Since 2012 and Prior                                                                                        |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 32            |          |          |
| Yolanda (Block I)                                                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 23            |          |          |
| Yolanda (Block I) | Suspended Since 2015 and 2016                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 1             |          |          |
| Yolanda (Block I) | Suspended Since 2013 and 2014                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 6             |          |          |
| Yolanda (Block I) | Suspended Since 2012 and Prior                                                                                         |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 16            |          |          |
| YoYo (YoYo Block)                                                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 55            |          |          |
| YoYo (YoYo Block) | Suspended Since 2015 and 2016                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 4             |          |          |
| YoYo (YoYo Block) | Suspended Since 2013 and 2014                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 6             |          |          |
| YoYo (YoYo Block) | Suspended Since 2012 and Prior                                                                                         |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 45            |          |          |
| Leviathan-1 Deep                                                                                                                           |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 91            |          |          |
| Leviathan-1 Deep | Suspended Since 2015 and 2016                                                                                           |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 8             |          |          |
| Leviathan-1 Deep | Suspended Since 2013 and 2014                                                                                           |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 10            |          |          |
| Leviathan-1 Deep | Suspended Since 2012 and Prior                                                                                          |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 73            |          |          |
| Dalit                                                                                                                                      |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 32            |          |          |
| Dalit | Suspended Since 2015 and 2016                                                                                                      |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 3             |          |          |
| Dalit | Suspended Since 2013 and 2014                                                                                                      |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 5             |          |          |
| Dalit | Suspended Since 2012 and Prior                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 24            |          |          |
| Cyprus                                                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 97            |          |          |
| Cyprus | Suspended Since 2015 and 2016                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 15            |          |          |
| Cyprus | Suspended Since 2013 and 2014                                                                                                     |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 52            |          |          |
| Cyprus | Suspended Since 2012 and Prior                                                                                                    |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 30            |          |          |
| Projects less than $20 million                                                                                                             |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 18            |          |          |
| Projects less than $20 million | Suspended Since 2015 and 2016                                                                             |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | (9)           |          |          |
| Projects less than $20 million | Suspended Since 2013 and 2014                                                                             |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | 21            |          |          |
| Projects less than $20 million | Suspended Since 2012 and Prior                                                                            |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling                                       | $ 6           |          |          |
| Cyprus Block 12                                                                                                                            |          |          |          |
| **Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]**                                                   |          |          |          |
| Ownership interest sold                                                                                                                    | 35.00%        |          |          |

| X                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Disposal Group, Not Discontinued Operation, Percentage Sold
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph b -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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