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Impact of New Accounting Standards and Interpretations Impact of New Accounting Standards and Interpretations (Details) - USD ($)
$ in Millions
9 Months Ended
Jun. 30, 2020
Oct. 01, 2019
Sep. 30, 2018
Accounting Changes and Error Corrections [Abstract]      
Restricted cash     $ 13
Reclassification from Operating and maintenance expense to Other income $ 193    
Operating Lease, Asset   $ 205  
Operating Lease, Liability   $ 210