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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Allowance for Uncollectible Accounts    
Period of time for customers to fulfill payment arrangements 90 days  
Allowance for uncollectible accounts - receivables $ 1 $ 1
Loans receivable $ 130 117
Allowance for uncollectible accounts - loans   $ 8