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Capital Stock - Additional Information (Detail) - USD ($)
 12 Months Ended
Jan. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Class of Stock [Line Items]        
Common stock, shares authorized   5,000,000,000 5,000,000,000  
Preferred stock, shares authorized   500,000,000    
Preferred stock, shares issued   0 0 0
Preferred stock, shares outstanding   0 0 0
Cost of shares repurchased   $ 2,202,000,000 $ 2,601,000,000 $ 3,622,000,000
Repurchase of Common Stock   $ 2,174,000,000 $ 2,601,000,000 $ 3,622,000,000
Common Class A        
Class of Stock [Line Items]        
Common stock reserved for stock option and other stock awards   123,000,000    
Stock repurchase value   $ 13,700,000,000    
Number of shares repurchased   50,598,902 61,972,713 91,875,878
Average cost of shares repurchased   $ 43.51    
Cost of shares repurchased   $ 2,200,000,000    
Stock repurchase remaining amount   600,000,000    
Common Class A | Subsequent Event        
Class of Stock [Line Items]        
Stock repurchase value $ 100,000,000      
Repurchase of Common Stock 28,000,000      
Stock repurchase remaining amount 6,500,000,000      
Common Class A | Share Repurchase Program amended July 29, 2015 | Subsequent Event        
Class of Stock [Line Items]        
Stock repurchase value 19,700,000,000      
Increase in share repurchase value $ 6,000,000,000      
Stock repurchase expiration date Dec. 31, 2020      
Common Class A | Prior to January 1, 2017        
Class of Stock [Line Items]        
Stock repurchase value   $ 10,800,000,000