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Benefit Plans - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Oct. 31, 2017
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]        
Assumed health care trend rate   7.00% 6.60%  
Ultimate health care trend rate beginning in 2024   5.00% 5.00%  
Percent of total assets domestic plans   65.00%    
Cost of the savings incentive plan   $ 67 $ 61 $ 54
Fixed Income Funds        
Defined Benefit Plan Disclosure [Line Items]        
Company's Target allocation percentage for asset mix   40.00%    
Diversified        
Defined Benefit Plan Disclosure [Line Items]        
Company's Target allocation percentage for asset mix   28.00%    
Equity securities        
Defined Benefit Plan Disclosure [Line Items]        
Company's Target allocation percentage for asset mix   32.00%    
Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets at fair value   $ 1,932 1,855 1,732
Pension plan projected benefit obligations   2,647 2,719 2,426
Estimated net actuarial loss that will be amortized from accumulated other comprehensive income   (76)    
Estimated prior service credit costs that will be amortized from accumulated other comprehensive income   (13)    
Employer contribution   54 145  
Other Postretirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan projected benefit obligations   165 184 $ 186
Estimated prior service credit costs that will be amortized from accumulated other comprehensive income   (5)    
United States | Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets at fair value   1,254 1,231  
United States | Pension Plans | Equity securities        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets at fair value   369 348  
Foreign Plans | Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets at fair value   678 624  
Pension plan projected benefit obligations   $ 917 951  
Percent of total plan assets foreign plans   35.00%    
Foreign Plans | Pension Plans | Equity securities        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets at fair value   $ 256 $ 228  
Subsequent Event [Member] | United States | Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Employer contribution $ 112