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Supplemental Guarantor Condensed Consolidating Financial Statements - Additional Information (Details) - USD ($)
$ in Millions
6 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Sep. 30, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]      
Parent's total ownership, percentage 100.00%    
Parent      
Condensed Financial Statements, Captions [Line Items]      
Pension and retiree benefits, parent obligation $ 686   $ 708
Proceeds from investment in subsidiary 1 $ 17  
Subsidiaries      
Condensed Financial Statements, Captions [Line Items]      
Debt and capital lease obligations, subsidiary portion $ 13   $ 24