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Stock-Based Compensation - Annual Activity Of Stock Options Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Aggregate Intrinsic Value - Exercised $ 6us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue $ 23us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue $ 11us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options   $ 3us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions