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Pension and Postretirement Plans - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Jun. 30, 2023
Jun. 30, 2022
Retirement Benefits [Abstract]        
Net actuarial gain (loss) $ 6 $ (87) $ (17) $ (104)