| **Derivative Instruments and Hedging Activities (Details 2) (USD $)In Millions, unless otherwise specified** | 3 Months Ended | 6 Months Ended |        |
|--------------------------------------------------------------------------------------------------------------|----------------|----------------|--------|
||
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| Derivative Asset, Fair Value                                                                                 | $ 2            |           | $ 2    |   | $ 17 |
| Derivative Liability, Fair Value                                                                             | 288            |           | 288    |   | 75 |
| (Gain) Loss on Commodity Derivative Instruments                                                              | 236            | (161)          | 311    | (89) |   |
| Cash (Received) Paid in Settlement of Commodity Derivative Instruments                                       | 49             | (2)            | 83     | (9) |   |
| Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments                                          | 187            | (159)          | 228    | (80) |   |
| AOCL amount, net of tax, to be reclassified to interest expense over life of debt                            |           |           | (23)   |   |   |
| Current Assets                                                                                               |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| Derivative Asset, Fair Value                                                                                 | 0              |           | 0      |   | 1 |
| Current Liabilities                                                                                          |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| Derivative Liability, Fair Value                                                                             | 199            |           | 199    |   | 65 |
| Noncurrent Assets                                                                                            |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| Derivative Asset, Fair Value                                                                                 | 2              |           | 2      |   | 16 |
| Noncurrent Liabilities                                                                                       |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| Derivative Liability, Fair Value                                                                             | 89             |           | 89     |   | 10 |
| Crude Oil [Member]                                                                                           |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| (Gain) Loss on Commodity Derivative Instruments                                                              | 238            | (118)          | 292    | (69) |   |
| Cash (Received) Paid in Settlement of Commodity Derivative Instruments                                       | 46             | 6              | 73     | 14 |   |
| Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments                                          | 192            | (124)          | 219    | (83) |   |
| Natural Gas [Member]                                                                                         |           |           |   |   |   |
| **Derivatives, Fair Value [Line Items]**                                                                     |           |           |   |   |   |
| (Gain) Loss on Commodity Derivative Instruments                                                              | (2)            | (43)           | 19     | (20) |   |
| Cash (Received) Paid in Settlement of Commodity Derivative Instruments                                       | (3)            | (8)            | 10     | (23) |   |
| Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments                                          | $ (5)          | $ (35)         | $ 9    | $ 3 |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226000-175313Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.
+ References
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| X                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.
+ References
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