2.2.0.25falsefalse009080 - Disclosure - Employee Benefit Plans (Details)truefalseIn Millionsfalse1falsefalseUSDfalsefalse1/1/2011 - 3/31/2011 USD ($) USD ($) / shares $c20110101to20110331http://www.sec.gov/CIK0000072207duration2011-01-01T00:00:002011-03-31T00:00:00U003Standardhttp://www.xbrl.org/2003/instancesharesxbrli0U001Standardhttp://www.xbrl.org/2003/iso4217USDiso42170U002Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0U004Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$2falsefalseUSDfalsefalse1/1/2010 - 3/31/2010 USD ($) USD ($) / shares $c20100101to20100331http://www.sec.gov/CIK0000072207duration2010-01-01T00:00:002010-03-31T00:00:00U001Standardhttp://www.xbrl.org/2003/iso4217USDiso42170U003Standardhttp://www.xbrl.org/2003/instancesharesxbrli0U002Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0U004Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$2true0nbl_NotesToFinancialStatementsAbstractnblfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseNotes to Financial Statements [Abstract]3false0us-gaap_DefinedBenefitPlanServiceCostus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse40000004falsetruefalsefalsefalse2truefalsefalse40000004falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph a, h falsefalseService Cost4false0us-gaap_DefinedBenefitPlanInterestCostus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse30000003falsefalsefalsefalsefalse2truefalsefalse30000003falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph a, h falsefalseInterest Cost5false0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssetsus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsetruenegated1truefalsefalse-4000000-4falsefalsefalsefalsefalse2truefalsefalse-3000000-3falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryAn amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph h falsefalseExpected Return on Plan Assets6false0nbl_DefinedBenefitPlanOthernblfalsedebitdurationOther changes to the entity's defined benefit pension plan's projected benefit obligation or a defined benefit postretirement...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse20000002falsefalsefalsefalsefalse2truefalsefalse10000001falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryOther changes to the entity's defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation as of the balance sheet date.No authoritative reference available.falsefalseOther7false0us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalsetotallabel1truefalsefalse50000005falsefalsefalsefalsefalse2truefalsefalse50000005falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph h truefalseNet Periodic Benefit Cost8false0us-gaap_PensionContributionsus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse20000002falsetruefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe amount of cash or cash equivalents contributed by the entity to fund its pension plans.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 falsefalseCash contributions to pension plan27Employee Benefit Plans (Details) (USD $)MillionsUnKnownUnKnownUnKnownfalsetrue