Debt - Schedule of Debt (Details) - USD ($) $ in Millions	Jun. 30, 2025	Sep. 30, 2024	Jun. 30, 2024
Debt Instrument [Line Items]
Notes payable	$ 4,002.9		$ 3,004.1
Less: current portion	(1.0)		(1.1)
Less: unamortized discount and debt issuance costs	(27.2)		(11.7)
Total long-term debt	$ 3,974.7		2,991.3
Fixed-rate 3.375% notes due September 15, 2025 | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	3.375%
Effective Interest Rate	3.47%
Notes payable	$ 0.0		1,000.0
Fixed-rate 1.700% notes due May 15, 2028 | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	1.70%
Effective Interest Rate	1.85%
Notes payable	$ 1,000.0		1,000.0
Fixed-rate 1.250% notes due September 1, 2030 | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	1.25%
Effective Interest Rate	1.83%
Notes payable	$ 1,000.0		1,000.0
Fixed-rate 4.750% notes due May 8, 2032 | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	4.75%
Effective Interest Rate	4.95%
Notes payable	$ 1,000.0		0.0
Fixed-rate 4.450% notes due September 9, 2034 | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage	4.45%	4.45%
Effective Interest Rate	4.75%
Notes payable	$ 1,000.0		0.0
Other
Debt Instrument [Line Items]
Notes payable	$ 2.9		$ 4.1