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Stock Plans - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions
 1 Months Ended 9 Months Ended 12 Months Ended
Jul. 29, 2015
Oct. 31, 2017
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2013
Class of Stock [Line Items]            
Cost of shares repurchased     $ 1,817,000,000   $ 2,601,000,000  
Repurchase of Common Stock     $ 1,786,000,000 $ 1,727,000,000    
Common Class A            
Class of Stock [Line Items]            
Number of shares repurchased     42      
Average cost of shares repurchased     $ 43.67      
Cost of shares repurchased     $ 1,817,000,000      
Stock repurchase remaining amount     1,000,000,000      
Common Class A | Share Repurchase Program amended July 29, 2015            
Class of Stock [Line Items]            
Stock repurchase value $ 13,700,000,000          
Increase in share repurchase value $ 6,000,000,000          
Stock repurchase expiration date Dec. 31, 2018          
Common Class A | Prior to January 1, 2016            
Class of Stock [Line Items]            
Stock repurchase value     $ 10,800,000,000     $ 7,700,000,000
Subsequent Event | Common Class A            
Class of Stock [Line Items]            
Repurchase of Common Stock   $ 31,000,000