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Fair Value Measurements (Schedule Of Available For Sale Securities) (Details) - USD ($)
$ in Millions
Jun. 30, 2018
Sep. 30, 2017
U.S. treasury and agency    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost Basis $ 46 $ 47
Fair Value 45 47
Unrealized Gain (Loss) (1) 0
Corporate and asset-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost Basis 53 51
Fair Value 53 51
Unrealized Gain (Loss) $ 0 $ 0