v3.3.0.814
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Current year actuarial (gain) loss $ 122 $ 27 $ (187)
Amortization of prior service credit/(cost) 1 8 $ (16)
Pension benefits      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Current year actuarial (gain) loss 119 18  
Amortization of actuarial (loss) gain (8) (4)  
Current year prior service credit 0 (3)  
Amortization of prior service credit/(cost) 7 11  
Total recognized in other comprehensive income 118 22  
Total recognized in net periodic benefit cost and other comprehensive income 134 35  
Other postretirement benefits      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Current year actuarial (gain) loss 0 (2)  
Amortization of actuarial (loss) gain 2 1  
Current year prior service credit 0 0  
Amortization of prior service credit/(cost) 3 3  
Total recognized in other comprehensive income 5 2  
Total recognized in net periodic benefit cost and other comprehensive income $ 1 $ (1)