Long-Term Debt - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Debt Instrument [Line Items]
Long-term debt, maturing in 2025	$ 520,000,000
Long-term debt, maturing in 2026	538,000,000
Long-term debt, maturing in 2027	746,000,000
Long-term debt, maturing in 2028	497,000,000
Interest paid on long-term debt	200,000,000	$ 199,000,000	$ 156,000,000
Repayments of long-term debt	741,000,000	522,000,000	$ 308,000,000
2.625% notes due February 2023 | Notes Payable
Debt Instrument [Line Items]
Repayments of long-term debt	$ 500,000,000	$ 500,000,000
Notes interest rate, percentage	2.625%	2.625%
2.625% notes due February 2023 | Notes Payable | AspenTech
Debt Instrument [Line Items]
Repayments of long-term debt	$ 264,000,000
2.0% notes due December 2028 | Notes Payable
Debt Instrument [Line Items]
Notes interest rate, percentage	2.00%			2.00%
Debt, face amount				$ 1,000,000,000
2.20% notes due December 2031 | Notes Payable
Debt Instrument [Line Items]
Notes interest rate, percentage	2.20%			2.20%
Debt, face amount				$ 1,000,000,000
2.80% notes due December 2051 | Notes Payable
Debt Instrument [Line Items]
Notes interest rate, percentage	2.80%			2.80%
Debt, face amount				$ 1,000,000,000