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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]      
Rental expense $ 61us-gaap_OperatingLeasesRentExpenseMinimumRentals $ 70us-gaap_OperatingLeasesRentExpenseMinimumRentals $ 50us-gaap_OperatingLeasesRentExpenseMinimumRentals