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Long-Term Debt - Long-Term Debt Denominated by Currencies (Detail) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Long-term debt $ 1,701 $ 1,451
U.S. dollar [Member]    
Debt Instrument [Line Items]    
Long-term debt 1,634 1,380
Euro [Member]    
Debt Instrument [Line Items]    
Long-term debt $ 67 $ 71