Basis Of Presentation	6 Months Ended
Jun. 30, 2012
Basis Of Presentation [Abstract]
Basis Of Presentation	Basis of Presentation Presentation. In the opinion of management, the consolidated financial statements of the Company as of June 30, 2012 and for the three and six months ended June 30, 2012 and 2011 include all adjustments and accruals, consisting only of normal recurring accrual adjustments, which are necessary for a fair presentation of the results for the interim periods. These interim results are not necessarily indicative of results for a full year. Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States ("GAAP") have been condensed or omitted in this Report pursuant to the rules and regulations of the United States Securities and Exchange Commission (the "SEC"). These consolidated financial statements should be read together with the consolidated financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2011. Certain reclassifications have been made to the 2011 financial statement and footnote amounts in order to conform to the 2012 presentation. On May 6, 2008, the Company recognized a noncash gain on the sale of Pioneer Southwest Energy Partners L.P.'s ("Pioneer Southwest," a majority-owned and consolidated subsidiary) common units as a component of additional paid-in capital in stockholders' equity. In accordance with the Financial Accounting Standards Board ("FASB") Accounting Standards Codification (“ASC”) Topic 740 Income Taxes, deferred income taxes of $49.1 million should be recognized for the future tax effects arising from the noncash gain on the sale of the Pioneer Southwest common units, with a corresponding decrease to additional paid-in capital. The Company recorded the deferred income taxes associated with this transaction in June 2012. The effect of this adjustment is immaterial to the accompanying financial statements. Revision for deferred income taxes. The accompanying consolidated balance sheet as of December 31, 2011 has been revised for a change in the classification of deferred income taxes associated with the Company's unrealized current derivative net gains as of December 31, 2011. The noncash revisions resulted in a $77.0 million decrease in current deferred tax assets, a $57.7 million increase in current deferred tax liabilities and a $134.7 million decrease in noncurrent deferred tax liabilities from the amounts previously reported at December 31, 2011. Such revisions were made to appropriately reflect the impact on deferred income taxes based on the expected settlement periods related to derivatives, which remained subject to market risk as of December 31, 2011. See "- Derivatives and hedging," below and Notes F and H for more information about derivative fair values and market risk. Derivatives and hedging. All derivatives are recorded in the accompanying consolidated balance sheets at their estimated fair values. See Note E for further information regarding the fair value of the Company's derivatives. Effective February 1, 2009, the Company discontinued hedge accounting on all of its then-existing derivative hedge contracts. Changes in the fair value of effective cash flow hedges prior to the Company's discontinuance of hedge accounting were recorded as a component of accumulated other comprehensive income or loss ("AOCI - Hedging"), in the equity section of the Company's consolidated balance sheets, and were transferred to earnings during the same periods in which the hedged transactions were recognized in the Company's earnings. As of June 30, 2012, all of the hedge gains or losses that were previously deferred in AOCI - Hedging have been transferred to earnings. The Company now recognizes all changes in the fair values of its derivative contracts as gains or losses in the earnings of the periods in which they occur. The Company classifies the fair value amounts of derivative assets and liabilities executed under master netting arrangements as net current or noncurrent derivative assets or net current or noncurrent derivative liabilities, whichever the case may be, by commodity and counterparty. Net derivative asset values are determined, in part, by utilization of the derivative counterparties' credit-adjusted risk-free rate curves and net derivative liabilities are determined, in part, by utilization of the Company's and Pioneer Southwest's credit-adjusted risk-free rate curves. The credit-adjusted risk-free rate curves for the Company and its counterparties are generally based on their independent market-quoted credit default swap rate curves plus the United States Treasury Bill yield curve as of the valuation date. Pioneer Southwest's credit-adjusted risk-free rate curve is based on independent market-quoted forward London Interbank Offered Rate ("LIBOR") curves plus 162.5 basis points, representing Pioneer Southwest's borrowing rate. Impairment of assets. The Company reviews its long-lived assets for impairment, including oil and gas properties, whenever events or circumstances indicate that their carrying values may not be fully recoverable. If the carrying value of long-lived assets is determined to be impaired, it is reduced to its estimated fair value with a corresponding charge to pretax earnings in the period in which it is determined to be impaired. See Note O for additional information about the Company's impairment charge for the three and six months ended June 30, 2012, and future impairment risk. Goodwill is assessed for impairment whenever events or circumstances indicate that impairment of the carrying value of goodwill is likely, but no less often than annually. If the carrying value of goodwill is determined to be impaired, it is reduced for the impaired value with a corresponding charge to pretax earnings in the period in which it is determined to be impaired. During the third quarter of 2011, the Company performed its annual assessment of goodwill impairment and determined that there was no impairment. New accounting pronouncement. In September 2011, the FASB issued Accounting Standards Update ("ASU") No. 2011-08 Intangibles - Goodwill and Other (Topic 350) ("ASU 2011-08"). ASU 2011-08 amended FASB ASC Topic 350 to permit an entity to first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test. The more-likely-than-not threshold is defined as having a likelihood of more than 50 percent. ASU 2011-08 became effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. The adoption of ASU 2011-08 did not impact the carrying value of the Company's goodwill. See Note O for information regarding the Company's impairment assessments.

Basis of Presentation

Presentation. In the opinion of management, the consolidated financial statements of the Company as of June 30, 2012 and for the three and six months ended June 30, 2012 and 2011 include all adjustments and accruals, consisting only of normal recurring accrual adjustments, which are necessary for a fair presentation of the results for the interim periods. These interim results are not necessarily indicative of results for a full year.

Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States ("GAAP") have been condensed or omitted in this Report pursuant to the rules and regulations of the United States Securities and Exchange Commission (the "SEC"). These consolidated financial statements should be read together with the consolidated financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2011.

Certain reclassifications have been made to the 2011 financial statement and footnote amounts in order to conform to the 2012 presentation.

On May 6, 2008, the Company recognized a noncash gain on the sale of Pioneer Southwest Energy Partners L.P.'s ("Pioneer Southwest," a majority-owned and consolidated subsidiary) common units as a component of additional paid-in capital in stockholders' equity. In accordance with the Financial Accounting Standards Board ("FASB") Accounting Standards Codification (“ASC”) Topic 740 Income Taxes, deferred income taxes of $49.1 million should be recognized for the future tax effects arising from the noncash gain on the sale of the Pioneer Southwest common units, with a corresponding decrease to additional paid-in capital. The Company recorded the deferred income taxes associated with this transaction in June 2012. The effect of this adjustment is immaterial to the accompanying financial statements.

Revision for deferred income taxes. The accompanying consolidated balance sheet as of December 31, 2011 has been revised for a change in the classification of deferred income taxes associated with the Company's unrealized current derivative net gains as of December 31, 2011. The noncash revisions resulted in a $77.0 million decrease in current deferred tax assets, a $57.7 million increase in current deferred tax liabilities and a $134.7 million decrease in noncurrent deferred tax liabilities from the amounts previously reported at December 31, 2011. Such revisions were made to appropriately reflect the impact on deferred income taxes based on the expected settlement periods related to derivatives, which remained subject to market risk as of December 31, 2011. See "- Derivatives and hedging," below and Notes F and H for more information about derivative fair values and market risk.

Derivatives and hedging. All derivatives are recorded in the accompanying consolidated balance sheets at their estimated fair values. See Note E for further information regarding the fair value of the Company's derivatives. Effective February 1, 2009, the Company discontinued hedge accounting on all of its then-existing derivative hedge contracts. Changes in the fair value of effective cash flow hedges prior to the Company's discontinuance of hedge accounting were recorded as a component of accumulated other comprehensive income or loss ("AOCI - Hedging"), in the equity section of the Company's consolidated balance sheets, and were transferred to earnings during the same periods in which the hedged transactions were recognized in the Company's earnings. As of June 30, 2012, all of the hedge gains or losses that were previously deferred in AOCI - Hedging have been transferred to earnings. The Company now recognizes all changes in the fair values of its derivative contracts as gains or losses in the earnings of the periods in which they occur.

The Company classifies the fair value amounts of derivative assets and liabilities executed under master netting arrangements as net current or noncurrent derivative assets or net current or noncurrent derivative liabilities, whichever the case may be, by commodity and counterparty. Net derivative asset values are determined, in part, by utilization of the derivative counterparties' credit-adjusted risk-free rate curves and net derivative liabilities are determined, in part, by utilization of the Company's and Pioneer Southwest's credit-adjusted risk-free rate curves. The credit-adjusted risk-free rate curves for the Company and its counterparties are generally based on their independent market-quoted credit default swap rate curves plus the United States Treasury Bill yield curve as of the valuation date. Pioneer Southwest's credit-adjusted risk-free rate curve is based on independent market-quoted forward London Interbank Offered Rate ("LIBOR") curves plus 162.5 basis points, representing Pioneer Southwest's borrowing rate.

Impairment of assets. The Company reviews its long-lived assets for impairment, including oil and gas properties, whenever events or circumstances indicate that their carrying values may not be fully recoverable. If the carrying value of long-lived assets is determined to be impaired, it is reduced to its estimated fair value with a corresponding charge to pretax earnings in the period in which it is determined to be impaired. See Note O for additional information about the Company's impairment charge for the three and six months ended June 30, 2012, and future impairment risk.

Goodwill is assessed for impairment whenever events or circumstances indicate that impairment of the carrying value of goodwill is likely, but no less often than annually. If the carrying value of goodwill is determined to be impaired, it is reduced for the impaired value with a corresponding charge to pretax earnings in the period in which it is determined to be impaired. During the third quarter of 2011, the Company performed its annual assessment of goodwill impairment and determined that there was no impairment.

New accounting pronouncement. In September 2011, the FASB issued Accounting Standards Update ("ASU") No. 2011-08 Intangibles - Goodwill and Other (Topic 350) ("ASU 2011-08"). ASU 2011-08 amended FASB ASC Topic 350 to permit an entity to first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test. The more-likely-than-not threshold is defined as having a likelihood of more than 50 percent. ASU 2011-08 became effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. The adoption of ASU 2011-08 did not impact the carrying value of the Company's goodwill. See Note O for information regarding the Company's impairment assessments.