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Schedule of Unearned Compensation and Weighted Average Remaining Period for Outstanding Share-Based Awards (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unearned Compensation $ 62us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
RSUs  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unearned Compensation 55us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Weighted-Average Remaining Period (in years) 1 year 4 months 24 days
Restricted Stock  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unearned Compensation $ 7us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Weighted-Average Remaining Period (in years) 1 year 4 months 24 days