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Employee Incentive Plans, Long term Incentive Plans (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award      
Number of common shares authorized for issuance under Equity Incentive Plan 2,722,222us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized    
Number of common shares available for additional awards under Equity Incentive Plan 776,549us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant    
Non-employee directors time to vest in long-term incentive plan 1 year    
Time for executives and other employees to vest in long-term incentive plan 3 years    
Non-cash compensation expense $ 6.8us-gaap_AllocatedShareBasedCompensationExpense $ 6.6us-gaap_AllocatedShareBasedCompensationExpense $ 5.6us-gaap_AllocatedShareBasedCompensationExpense
Recognized tax benefit relating to non-cash compensation expense 2.5us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2.4us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2.1us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Summary of Activity      
Total grant-date fair value for shares granted 14.8kalu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodTotalFairValue 14.8kalu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodTotalFairValue 13.9kalu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodTotalFairValue
Total grant-date fair value for shares that vested 5.5us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue 5.1us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue 3.5us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
Stock Options      
Fully-vested options outstanding 16,645us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber 20,791us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber  
Exercise price of options to purchase common stock $ 80.01us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 80.01us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice  
Remaining contractual life of options outstanding 2 years 3 months 3 years 3 months  
Grant date fair value of options outstanding $ 39.90us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue    
Stock options granted 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross  
Stock options forfeited 4,146us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod  
Stock options expired   0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod  
Stock options exercised 0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised  
Vested Stock      
Common shares granted to non-employee directors 0.2us-gaap_StockIssuedDuringPeriodValueIssuedForServices 0.2us-gaap_StockIssuedDuringPeriodValueIssuedForServices 0.2us-gaap_StockIssuedDuringPeriodValueIssuedForServices
Common shares withheld and canceled 33,696us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation 40,075us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation 45,801us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Fabricated Products      
Share-based Compensation Arrangement by Share-based Payment Award      
Non-cash compensation expense 3.2us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_FabricatedProductsMember		 2.2us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_FabricatedProductsMember		 1.7us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_FabricatedProductsMember
All Other      
Share-based Compensation Arrangement by Share-based Payment Award      
Non-cash compensation expense 3.6us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_AllOtherMember		 4.4us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_AllOtherMember		 3.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_StatementBusinessSegmentsAxis
= kalu_AllOtherMember
Non-vested common shares      
Summary of Activity      
Outstanding Beginning Balance, Shares/Units 143,967us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Outstanding Beginning Balance, Weighted-Average Grant-Date Fair Value per Share $ 51.09us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Granted, shares/units 119,799us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 [1]    
Granted, Weighted-Average Grant-Date Fair Value per Share $ 66.42us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 [1]    
Vested, shares/units (64,493)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Vested, Weighted-Average Grant-Date Fair Value per Share $ 52.20us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Forfeited, shares/units (40,503)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 [1]    
Forfeited, Weighted-Average Grant-Date Fair Value per Share $ 60.21us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 [1]    
Outstanding Ending Balance, Shares/Units 158,770us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Outstanding Ending Balance, Weighted-Average Grant-Date Fair Value per Share $ 59.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		    
Restricted stock units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of common share received by the employee on vesting of restricted stock unit 1kalu_NumberOfCommonShareReceivedByEmployeeOnVestingOfRestrictedStockUnit
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Summary of Activity      
Outstanding Beginning Balance, Shares/Units 5,472us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Outstanding Beginning Balance, Weighted-Average Grant-Date Fair Value per Share $ 51.03us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Granted, shares/units 2,235us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [1]    
Granted, Weighted-Average Grant-Date Fair Value per Share $ 67.42us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [1]    
Vested, shares/units (2,350)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Vested, Weighted-Average Grant-Date Fair Value per Share $ 46.83us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Forfeited, shares/units 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [1]    
Forfeited, Weighted-Average Grant-Date Fair Value per Share $ 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [1]    
Outstanding Ending Balance, Shares/Units 5,357us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Outstanding Ending Balance, Weighted-Average Grant-Date Fair Value per Share $ 59.71us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Service-based non-vested common shares and restricted stock units      
Share-based Compensation Arrangement by Share-based Payment Award      
Non-cash compensation expense 3.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_RestrictedStockAndRestrictedStockUnitsMember		 4.3us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_RestrictedStockAndRestrictedStockUnitsMember		 3.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_RestrictedStockAndRestrictedStockUnitsMember
Unrecognized gross compensation costs 5.6us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= kalu_RestrictedStockAndRestrictedStockUnitsMember		    
Expected period (in years) over which the remaining gross compensation costs will be recognized 2 years 2 months 28 days    
Performance shares      
Share-based Compensation Arrangement by Share-based Payment Award      
Non-cash compensation expense 1.0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 2.3us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 1.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Unrecognized gross compensation costs 1.6us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		    
Expected period (in years) over which the remaining gross compensation costs will be recognized 1 year 0 months 1 day    
Summary of Activity      
Outstanding Beginning Balance, Shares/Units 562,554us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		    
Outstanding Beginning Balance, Weighted-Average Grant-Date Fair Value per Share $ 49.26us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		    
Granted, shares/units 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [1]    
Granted, Weighted-Average Grant-Date Fair Value per Share $ 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [1]    
Vested, shares/units (42,545)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		    
Vested, Weighted-Average Grant-Date Fair Value per Share $ 47.21us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		    
Forfeited, shares/units (28,613)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [1]    
Forfeited, Weighted-Average Grant-Date Fair Value per Share $ 51.44us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [1]    
Canceled, shares/units (137,820)kalu_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsCancelledInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [2]    
Canceled, Weighted-Average Grant-Date Fair Value per Share $ 46.65kalu_ShareBasedCompensationArrangementByShareBasedPaymentsAwardEquityInstrumentsOtherThanOptionsCancelledInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [2]    
Outstanding Ending Balance, Shares/Units 353,576us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 562,554us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Outstanding Ending Balance, Weighted-Average Grant-Date Fair Value per Share $ 50.35us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 $ 49.26us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Market-based shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award      
Non-cash compensation expense 1.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember
Unrecognized gross compensation costs $ 4.4us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		    
Expected period (in years) over which the remaining gross compensation costs will be recognized 2 years 1 month 14 days    
Summary of Activity      
Outstanding Beginning Balance, Shares/Units 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		    
Outstanding Beginning Balance, Weighted-Average Grant-Date Fair Value per Share $ 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		    
Granted, shares/units 160,868us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 [1]    
Granted, Weighted-Average Grant-Date Fair Value per Share $ 83.18us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 [1]    
Vested, shares/units 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		    
Vested, Weighted-Average Grant-Date Fair Value per Share $ 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		    
Forfeited, shares/units (10,645)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 [1]    
Forfeited, Weighted-Average Grant-Date Fair Value per Share $ 83.18us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 [1]    
Outstanding Ending Balance, Shares/Units 150,223us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		  
Outstanding Ending Balance, Weighted-Average Grant-Date Fair Value per Share $ 83.18us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		 $ 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember		  
Minimum | Performance shares      
Share-based Compensation Arrangement by Share-based Payment Award      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 0.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Minimum | Market-based shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 0.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Maximum | Performance shares      
Share-based Compensation Arrangement by Share-based Payment Award      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 200.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Maximum | Market-based shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 200.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= kalu_MarketbasedsharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
[1] For EVA-Based Performance Shares and TSR-Based Performance Shares, the number of shares granted and forfeited are presented at their maximum payout.
[2] For EVA-Based Performance Shares and TSR-Based Performance Shares, canceled represents the number of shares that did not vest due to EVA or TSR performance results falling below those required for maximum payout.