XML 19 R70.htm IDEA: XBRL DOCUMENT
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Fair Value Measurements, Fair Value Hierarchy Table (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Financial Assets: |  |  |  |
Derivative Asset | $ 85.7 us-gaap_DerivativeAssets |  | $ 81.8 us-gaap_DerivativeAssets |
Deferred compensation plan assets | 7.3 us-gaap_DeferredCompensationPlanAssets |  | 6.5 us-gaap_DeferredCompensationPlanAssets |
Investment Percentage in Industrial Sector | 51.00%kalu_InvestmentPercentageInIndustrialSector |  | 56.00%kalu_InvestmentPercentageInIndustrialSector |
Investment Percentage in Financial Sector | 37.00%kalu_InvestmentPercentageInFinancialSector |  | 35.00%kalu_InvestmentPercentageInFinancialSector |
Investment Percentage in Utilities Sector | 12.00%kalu_InvestmentPercentageInUtilitiesSector |  | 9.00%kalu_InvestmentPercentageInUtilitiesSector |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (96.8)us-gaap_DerivativeLiabilities |  | (86.1)us-gaap_DerivativeLiabilities |
Fair Value, Measurements, Recurring [Member] |  |  |  |
Financial Assets: |  |  |  |
Cash and cash equivalents | 177.7 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1] | 169.5 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1]
Deferred compensation plan assets | 7.3 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 6.5 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Assets | 1,171.1 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,158.2 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Financial Liabilities: |  |  |  |
Convertible Notes, including Bifurcated Conversion Feature | (263.3)us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (260.0)us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Liabilities | (604.6)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (601.5)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 394.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] | 375.0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Mortgage backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 30.1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 25.9 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Corporate debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 75.4 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [3] | 78.2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [3]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 191.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [4] | 175.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [4]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | United States Treasuries |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 39.5 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 43.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Municipal debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 1.8 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1.6 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Cash and money market investments |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 19.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [5] | 36.8 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [5]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Asset backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 8.1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8.5 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 26.6 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6] | 26.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6]
Fair Value, Measurements, Recurring [Member] | Senior Notes |  |  |  |
Financial Liabilities: |  |  |  |
Senior Notes | (244.5)us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (255.4)us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Debt Securities |  |  |  |
Financial Assets: |  |  |  |
Short-term investments | 114.0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |  | 129.5 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
Fair Value, Measurements, Recurring [Member] | Aluminum | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.1 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (4.2)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (1.8)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Aluminum | Midwest premium swap contracts |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 1.0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1.1 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Natural Gas | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (6.2)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (0.8)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Electricity | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (1.7)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (0.4)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Foreign Currency | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.1 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ForeignCurrencyMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Hedges Relating to the Convertible Notes | Call Options |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 84.7 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 79.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature |  |  |  |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (84.7)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (83.1)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 |  |  |  |
Financial Assets: |  |  |  |
Cash and cash equivalents | 29.5 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 57.7 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1]
Deferred compensation plan assets | 0 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Assets | 123.2 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 171.6 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Financial Liabilities: |  |  |  |
Convertible Notes, including Bifurcated Conversion Feature | (263.3)us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (260.0)us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Liabilities | (507.8)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (515.4)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 54.0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] | 57.0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Mortgage backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Corporate debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [4]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | United States Treasuries |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Municipal debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Cash and money market investments |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 19.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [5] | 36.8 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [5]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Asset backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 20.4 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6] | 20.1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6]
Fair Value, Measurements, Recurring [Member] | Level 1 | Senior Notes |  |  |  |
Financial Liabilities: |  |  |  |
Senior Notes | (244.5)us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (255.4)us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Debt Securities |  |  |  |
Financial Assets: |  |  |  |
Short-term investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Aluminum | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Aluminum | Midwest premium swap contracts |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Natural Gas | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Electricity | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Foreign Currency | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ForeignCurrencyMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Hedges Relating to the Convertible Notes | Call Options |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 1 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature |  |  |  |
Financial Liabilities: |  |  |  |
Derivative Liabilities | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 |  |  |  |
Financial Assets: |  |  |  |
Cash and cash equivalents | 148.2 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 111.8 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [1]
Short-term investments | 114.0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  |  |
Deferred compensation plan assets | 7.3 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 6.5 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Assets | 1,046.9 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 985.5 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Financial Liabilities: |  |  |  |
Convertible Notes, including Bifurcated Conversion Feature | 0 us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Liabilities | (96.8)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (86.1)us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 340.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2] | 318.0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [2]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Mortgage backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 30.1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 25.9 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Corporate debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 75.4 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [3] | 78.2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [3]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 191.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [4] | 175.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [4]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | United States Treasuries |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 39.5 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 43.3 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Municipal debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 1.8 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1.6 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Cash and money market investments |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Asset backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 8.1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8.5 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 6.2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6] | 6.2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = kalu_DiversifiedInvestmentFundsInRegisteredInvestmentCompaniesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | [6]
Fair Value, Measurements, Recurring [Member] | Level 2 | Senior Notes |  |  |  |
Financial Liabilities: |  |  |  |
Senior Notes | 0 us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Debt Securities |  |  |  |
Financial Assets: |  |  |  |
Short-term investments |  |  | 129.5 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Aluminum | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.1 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (4.2)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (1.8)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Aluminum | Midwest premium swap contracts |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = kalu_MidwestPremiumSwapContractsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_AluminumMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Natural Gas | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (6.2)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (0.8)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_NaturalGasMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Electricity | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (1.7)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |  | (0.4)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ElectricityMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Foreign Currency | Fixed priced contracts | Purchase |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset |  |  | 0.1 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_ForeignCurrencyMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_PositionAxis = us-gaap_LongMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Hedges Relating to the Convertible Notes | Call Options |  |  |  |
Financial Assets: |  |  |  |
Derivative Asset | 84.7 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 79.5 us-gaap_DerivativeAssets / us-gaap_DerivativeByNatureAxis = us-gaap_CallOptionMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Level 2 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature |  |  |  |
Financial Liabilities: |  |  |  |
Derivative Liabilities | (84.7)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (83.1)us-gaap_DerivativeLiabilities / us-gaap_DerivativeByNatureAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_DerivativeInstrumentRiskAxis = kalu_HedgesRelatingToNotesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Financial Assets: |  |  |  |
Cash and cash equivalents | 0 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Deferred compensation plan assets | 0 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DeferredCompensationPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Assets | 1.0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1.1 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Financial Liabilities: |  |  |  |
Convertible Notes, including Bifurcated Conversion Feature | 0 us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_ConvertibleDebtFairValueDisclosures / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Total Liabilities | 0 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Mortgage backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MortgageBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Corporate debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquityFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | United States Treasuries |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasurySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Municipal debt securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Cash and money market investments |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Asset backed securities |  |  |  |
Financial Assets: |  |  |  |
VEBAs and Canadian Pension Plan Assets | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies |  |  |  |
Financial Assets: |  |  |  |
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[1] | See Note 2 for components of cash and cash equivalents.
[2] | This category represents investments in various fixed income funds with multiple registered investment companies. Such funds invest in diversified portfolios, including (i) marketable fixed income securities such as (a) U.S. Treasury and other government and agency securities, (b) municipal bonds, (c) mortgage-backed securities, (d) asset-backed securities, (e) corporate bonds, notes and debentures in various sectors, (f) preferred and common stock, (g) investments in affiliated and other investment companies, (h) short-term investments and other net assets and (i) repurchase agreements and reverse repurchase agreements; (ii) other commingled investments; (iii) investment grade debt; (iv) fixed income instruments which may be represented by options, future contracts or swap agreements; and (v) cash and cash equivalents. The fair value of assets in this category is estimated using the net asset value per share of the investments.
[3] | This category represents investments in fixed income corporate securities in various sectors. Investments in the industrial, financial and utilities sectors in 2014 represented approximately 51%, 37% and 12% of the total portfolio in this category, respectively. Investments in the industrial, financial and utilities sectors in 2013 represented approximately 56%, 35% and 9% of the total portfolio in this category, respectively. The fair value of assets in this category is estimated using the net asset value per share of the investments.
[4] | This category represents investments in equity funds that invest in portfolios comprised of (i) equity and equity-related securities of U.S. and non-U.S. issuers across all market capitalization; (ii) common stock in investment trust funds; and (iii) other short-term investments. The fair value of assets in this category is determined by using quoted prices in active markets for investments considered Level 1 inputs and estimated using the net asset value per share of the investments for investments considered Level 2 inputs.
[5] | This category represents cash and investments in various money market funds.
[6] | The plan assets are invested in investment funds that hold a diversified portfolio of (i) U.S and international debt and equity securities; (ii) fixed income securities such as corporate bonds and government bonds; (iii) mortgage-related securities; and (iv) cash and cash equivalents. The fair value of assets in this category is estimated using the net asset value per share of the investments.

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