|**Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | Jun. 30, 2015                                                                                                                                                                                                                                                          | Jun. 30, 2014                                                                                                                                                                                                                                                         
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|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                        | $ 112                                                                                                                                                                                                                                                                 
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                        | 556                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                        | 0                                                                                                                                                                                                                                                                     
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                        | (130)                                                                                                                                                                                                                                                                 
|Quoted Prices in Active Markets (Level 1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | [1]                                                                                                                                                                                                                                                                    | 112                                                                                                                                                                                                                                                                   
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [1]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [1]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | [1]                                                                                                                                                                                                                                                                    | (130)                                                                                                                                                                                                                                                                 
|Significant Other Observable Inputs (Level 2)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | [2]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [2]                                                                                                                                                                                                                                                                    | 559                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [2]                                                                                                                                                                                                                                                                    | (3)                                                                                                                                                                                                                                                                   
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | [2]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Significant Unobservable Inputs (Level 3)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | [3]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [3]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [3]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | [3]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Adjustment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|**Financial Assets [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Mutual Fund Investments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | [4]                                                                                                                                                                                                                                                                    | 0                                                                                                                                                                                                                                                                     
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [4]                                                                                                                                                                                                                                                                    | (3)                                                                                                                                                                                                                                                                   
|**Financial Liabilities [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                       
|Commodity Derivative Instruments                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | [4]                                                                                                                                                                                                                                                                    | 3                                                                                                                                                                                                                                                                     
|Portion of Deferred Compensation Liability Measured at Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | [4]                                                                                                                                                                                                                                                                    | $ 0                                                                                                                                                                                                                                                                   
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|[1]
Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.[2]
Level 2 measurements are fair value measurements which use inputs, other than quoted prices included within Level 1, which are observable for the asset or liability, either directly or indirectly.[3]
Level 3 measurements are fair value measurements which use unobservable inputs.[4]
Amount represents the impact of netting provisions within our master agreements that allow us to net cash settle asset and liability positions with the same counterparty. | [1]                                                                                                                                                                                                                                                                    | Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.
|[2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Level 2 measurements are fair value measurements which use inputs, other than quoted prices included within Level 1, which are observable for the asset or liability, either directly or indirectly.                                                                  
|[3]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Level 3 measurements are fair value measurements which use unobservable inputs.                                                                                                                                                                                       
|[4]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Amount represents the impact of netting provisions within our master agreements that allow us to net cash settle asset and liability positions with the same counterparty.                                                                                            

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