2.2.0.25falsefalse2105 - Disclosure - Plan Assets - Additional Information (Detail)truefalsefalse1falsefalseUSDfalsefalse1/1/2010 - 12/31/2010 USD ($) / shares USD ($) $FROM_Jan01_2010_TO_Dec31_2010http://www.sec.gov/CIK0000773910duration2010-01-01T00:00:002010-12-31T00:00:00usdPerShrDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0MMboeStandardhttp://www.anadarko.com/20101231MMboeapc0BcfStandardhttp://www.anadarko.com/20101231Bcfapc0USDUSD$2falsefalseUSDfalsefalse1/1/2009 - 12/31/2009 USD ($) USD ($) / shares $FROM_Jan01_2009_TO_Dec31_2009http://www.sec.gov/CIK0000773910duration2009-01-01T00:00:002009-12-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170usdPerShrDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0MMboeStandardhttp://www.anadarko.com/20101231MMboeapc0PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$3falsefalseUSDfalsefalse1/1/2008 - 12/31/2008 USD ($) USD ($) / shares $FROM_Jan01_2008_TO_Dec31_2008http://www.sec.gov/CIK0000773910duration2008-01-01T00:00:002008-12-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0MMboeStandardhttp://www.anadarko.com/20101231MMboeapc0usdPerShrDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$4false0us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYearus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.10.1falsefalsefalsefalsefalse2truetruefalse0.090.09falsefalsefalsefalsefalse3falsetruefalse00falsefalsefalsefalsefalseOtherus-types:percentItemTypepureThe assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). 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