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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2014
Mar. 08, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock, authorized shares       8,900,000
Percentage of vesting in first anniversary 30.00%      
Percentage of vesting in second anniversary 30.00%      
Percentage of vesting in third anniversary 40.00%      
Stock based compensation outstanding units 22,305      
Cash settled awards   $ 1    
Net stock-based compensation expense $ 10 $ 8 $ 9  
Recognized stock-based compensation expense in connection with the modification of outstanding equity awards $ 5      
Closing common stock price $ 52.41      
Stock Options, Weighted Average Grant Date Fair Value, Granted $ 11.12      
Supplemental 401(k) Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Supplemental retirement savings plan, aggregate value of the accounts, shares 143,000 150,000    
Supplemental retirement savings plan aggregate value of the accounts paid in cash $ 1 $ 1    
Maximum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Cash settled awards $ 1      
Stock Options [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Percentage of exercise price equal to market price on the date of grant 100.00%      
Vesting period (in years) 3 years      
Expiration period, years 10 years      
Unrecognized compensation cost $ 2      
Weighted-average period, years 1 year      
Intrinsic value of options exercised $ 8 2 12  
Cash received from exercises $ 8 $ 4 $ 9  
Stock Options, Weighted Average Grant Date Fair Value, Granted $ 11.12 $ 15.68 $ 18.36  
Restricted Stock Units [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period (in years) 3 years      
Stock based compensation outstanding units [1] 732,000 735,000    
Unrecognized compensation cost $ 14      
Weighted-average period, years 1 year 4 months 24 days      
Estimated weighted average grant date fair value $ 40.51 $ 45.85 $ 47.63  
Intrinsic value of restricted stock units vested $ 15 $ 14 $ 17  
Restricted Stock        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period (in years) 3 years      
[1] The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.