Quarterly report pursuant to Section 13 or 15(d)

Amortized Cost and Estimated Fair Value of Marketable Securities by Contractual Maturity (Detail)

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Amortized Cost and Estimated Fair Value of Marketable Securities by Contractual Maturity (Detail) - USD ($)
$ in Millions
Sep. 30, 2018
Dec. 31, 2017
Cost    
Due in one year or less $ 230  
Due after one year through three years 424  
Due after three years through five years 21  
Due after five years 75  
Marketable Securities, Debt Maturities, Amortized Cost, Total 750  
Equity securities 2  
Total Amortized Cost 752 $ 736
Estimated Fair Value    
Due in one year or less 228  
Due after one year through three years 420  
Due after three years through five years 21  
Due after five years 73  
Marketable Securities, Debt Maturities, Fair Value, Total 742  
Equity securities 2  
Total Estimated Fair Value $ 744 $ 749