Debt and Other Financing Activities - Summary of Current and Long-term Debt (Parenthetical) (Details) € in Millions, $ in Millions	9 Months Ended	12 Months Ended
Jun. 30, 2025 EUR (€)	Sep. 30, 2024 EUR (€)	Jun. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)
Debt Instrument [Line Items]
Unamortized debt issuance expense, long-term debt			$ 10	$ 12
Current portion of long-term debt			$ 0	$ 0
3.375% Senior Notes, due 2031 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.375%	3.375%	3.375%	3.375%
Debt instrument, maturity year	2031	2031
2.00% Senior Notes Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%	2.00%	2.00%	2.00%
Debt instrument, maturity year	2028	2028
Principal amount \| €	€ 500	€ 500
6.875% Notes due 2043 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.875%	6.875%	6.875%	6.875%
Debt instrument, maturity year	2043	2043
6.50% Junior Subordinated Notes, Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.50%	6.50%	6.50%	6.50%
Debt instrument, maturity year	2029	2029

Debt instrument maturity year.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective long-term debt and presented as a direct reduction to long-term debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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