Debt - Summary of Debt Issuance Cost Amortization (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Notes due 2022 [Member]
Debt Instrument [Line Items]
Repayment of debt, accelerated accretion	$ 1
2022 Notes, 2043 Notes and 2029 Junior Debentures [Member]
Debt Instrument [Line Items]
Repayment of debt, accelerated accretion		$ 2

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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