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Marketable Securities - Changes in Value of Marketable Securities Reported in Current Assets on Consolidated Balance Sheets (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]      
Beginning Balance $ 335 $ 334  
Purchase 0 0 $ (333)
Sale 0 0 58
Change in fair value included in OCI   1  
Change in fair value recognized in earnings 0    
Foreign exchange result through OCI   0  
Ending Balance 335 335 334
U.S.Treasury Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Beginning Balance 335 334  
Purchase 0 0  
Sale 0 0  
Change in fair value included in OCI   1  
Change in fair value recognized in earnings 0    
Foreign exchange result through OCI   0  
Ending Balance $ 335 $ 335 $ 334