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Pension and Other Benefit Programs - Plan Assets Investment Policy Ranges for Major Asset Classes (Detail)
12 Months Ended
Sep. 30, 2017
Equity Securities  
Defined Benefit Plan Disclosure [Line Items]  
Asset allocation range, minimum 30.00%
Asset allocation range, maximum 60.00%
Fixed Income Investments  
Defined Benefit Plan Disclosure [Line Items]  
Asset allocation range, minimum 20.00%
Asset allocation range, maximum 40.00%
Alternative Investments  
Defined Benefit Plan Disclosure [Line Items]  
Asset allocation range, minimum 10.00%
Asset allocation range, maximum 30.00%
Cash & Money Market Funds  
Defined Benefit Plan Disclosure [Line Items]  
Asset allocation range, minimum 0.00%
Asset allocation range, maximum 10.00%