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Equity Affiliates - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]      
Dividends received from equity affiliates $ 16us-gaap_EquityMethodInvestmentDividendsOrDistributions $ 10us-gaap_EquityMethodInvestmentDividendsOrDistributions $ 3us-gaap_EquityMethodInvestmentDividendsOrDistributions
Equity method investments exceeding minimum value 202us-gaap_EquityMethodInvestments    
Equity method investment carrying amount over the book value 74us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity    
Minimum [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity method investments exceeding minimum value 5us-gaap_EquityMethodInvestments
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
Goodwill [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity method investment carrying amount over the book value $ 48us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_GoodwillMember
   
Other Than Goodwill [Member] | Minimum [Member]      
Schedule of Equity Method Investments [Line Items]      
Estimated useful life 5 years    
Other Than Goodwill [Member] | Maximum [Member]      
Schedule of Equity Method Investments [Line Items]      
Estimated useful life 45 years