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Equity - Treasury Stock (Detail) - USD ($)
 3 Months Ended 6 Months Ended 9 Months Ended 12 Months Ended 20 Months Ended
Dec. 01, 2016
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Feb. 28, 2017
Jun. 30, 2017
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock, value   $ 35,823,000       $ 35,823,000   $ 14,288,000    
Retirement of treasury stock, shares (in shares) 84,800,000                  
Retirement of treasury stock, amount               $ 1,950,000,000    
2017 Repurchase Program                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired (in shares)           0        
2017 Repurchase Program | Maximum                    
Equity, Class of Treasury Stock [Line Items]                    
Aggregate authorized amount of common stock to be repurchased                   $ 300,000,000
2015 Repurchase Plan Open Market Purchases And Accelerated Share Repurchase Agreement                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired (in shares)           0 0   54,300,000  
Treasury stock acquired, value                 $ 1,200,000,000  
2015 Repurchase Program | Maximum                    
Equity, Class of Treasury Stock [Line Items]                    
Aggregate authorized amount of common stock to be repurchased       $ 1,250,000,000.00            
2015 Repurchase Program Open Market Purchases                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired (in shares)         19,200,000          
Treasury stock acquired, value         $ 449,900,000          
Accelerated Share Repurchase Agreement                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired (in shares)       25,700,000       9,400,000    
Treasury stock acquired, value       $ 600,000,000            
Aggregate authorized amount of common stock to be repurchased       750,000,000.0            
Payments for repurchase of common stock       750,000,000            
Accelerated stock repurchases settled at a later date       $ 150,000,000            
Treasury Stock Associated with Deferred Compensation Plans                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired, value   0 $ 300,000     $ 3,400,000 $ 8,200,000      
Treasury stock, value   $ 17,700,000       $ 17,700,000        
Common Stock Withheld for Settlement of Employee Tax Liabilities                    
Equity, Class of Treasury Stock [Line Items]                    
Treasury stock acquired (in shares)           500,000 400,000      
Treasury stock acquired, value           $ 18,200,000 $ 7,500,000