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Employee Benefit Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of employees contributions maximum 50.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent    
Percentage of company matches of employees contributions maximum 3.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent    
Employee vesting period Two years of service    
Employer contributions for benefit plans $ 36us-gaap_DefinedContributionPlanCostRecognized $ 28us-gaap_DefinedContributionPlanCostRecognized $ 22us-gaap_DefinedContributionPlanCostRecognized