Accounting Changes (Details) - USD ($) $ in Millions	Sep. 30, 2023	Oct. 01, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity	$ 4,394		$ 6,074	$ 5,531
Common Stock, without par value | Cumulative effect of change in accounting - ASU 2020-06 (Note 3)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity		$ 6
Preferred Stock
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity	167		162	213
Preferred Stock | Cumulative effect of change in accounting - ASU 2020-06 (Note 3)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity		6	5
Retained earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity	$ 3,027		4,841	$ 4,081	$ 2,908
Retained earnings | Cumulative effect of change in accounting - ASU 2020-06 (Note 3)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity		$ 1	$ 1