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Shareholders' Equity (Common Stock Issued With The Exercise Of Stock Options) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Stockholders' Equity Note [Abstract]    
Shares issued (in shares) 0.6us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 0.7us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Proceeds from the exercise of stock options $ 12.4an_ShareBasedCompensationArrangementByShareBasedPaymentAwardTotalConsiderationExerciseOfStockOptions $ 15.3an_ShareBasedCompensationArrangementByShareBasedPaymentAwardTotalConsiderationExerciseOfStockOptions
Average exercise price per share (in dollars per share) $ 20.15us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 20.84us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice