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Fair Value Measurements Fair Value Disclosure, Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Instrument, Fair Value Disclosure $ 8,500 $ 8,600
Deferred compensation plan assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity Securities, FV-NI, Unrealized Gain (Loss) 7 1
Exchange Traded Funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity Securities, FV-NI, Unrealized Gain (Loss) 37 21
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Instrument, Fair Value Disclosure 200 200
Fair Value, Inputs, Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Instrument, Fair Value Disclosure $ 8,300 $ 8,400