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Shareholders' Equity (Schedule Of Accumulated Other Comprehensive Income Activity) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance $ (371.6)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax [1] $ (471.4)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax [1]  
Other comprehensive income before reclassifications, net of tax expense (146.5)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax [1] 72.3us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax [1]  
Amounts reclassified from accumulated other comprehensive (loss) income 22.6us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax [1] 27.5us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax [1]  
Net current period other comprehensive (loss) income (123.9)us-gaap_OtherComprehensiveIncomeLossNetOfTax [1] 99.8us-gaap_OtherComprehensiveIncomeLossNetOfTax [1] (56.4)us-gaap_OtherComprehensiveIncomeLossNetOfTax
Ending Balance (495.5)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax [1] (371.6)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax [1] (471.4)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax [1]
Other comprehensive income before reclassifications, tax (expense) benefit 76.4awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax (42.8)awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax  
Foreign Currency Translation Adjustments [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance 21.3us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1] 30.1us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1]  
Other comprehensive income before reclassifications, net of tax expense (29.6)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1] (8.8)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1]  
Net current period other comprehensive (loss) income (29.6)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1] (8.8)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1]  
Ending Balance (8.3)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1] 21.3us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedTranslationAdjustmentMember		 [1]  
Derivative Adjustments [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance (0.7)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 (19.2)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Other comprehensive income before reclassifications, net of tax expense 1.1us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 18.3us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Amounts reclassified from accumulated other comprehensive (loss) income (4.4)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 0.2us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Net current period other comprehensive (loss) income (3.3)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 18.5us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Ending Balance (4.0)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 (0.7)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Other comprehensive income before reclassifications, tax (expense) benefit (0.8)awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		 (9.5)awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		  
Pension And Postretirement Adjustments [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance (392.2)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 (482.3)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
Other comprehensive income before reclassifications, net of tax expense (118.0)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 62.8us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
Amounts reclassified from accumulated other comprehensive (loss) income 27.0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 27.3us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
Net current period other comprehensive (loss) income (91.0)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 90.1us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
Ending Balance (483.2)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 (392.2)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
Other comprehensive income before reclassifications, tax (expense) benefit $ 77.2awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		 $ (34.6)awi_OtherComprehensiveIncomeLossBeforeReclassificationsTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		  
[1] Amounts are net of tax