Supplemental Information (Shareholder Activism-Related Costs) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Restructuring Cost and Reserve [Line Items]
Shareholder activism-related costs			$ 86.3	$ 0.0	$ 0.0
Shareholder activism-related costs, after tax			71.7
Professional fees			31.9
Charge for severance and other postemployment benefits			123.7	$ 57.0	$ 27.0
Mantle Ridge LP and Affiliates Transaction | Affiliated Entity
Restructuring Cost and Reserve [Line Items]
Cost for cash reimbursement	$ 24.7		24.7
Executive Separation Costs
Restructuring Cost and Reserve [Line Items]
CEO separation costs			29.7
Share-based payment arrangement, accelerated cost			22.4
Charge for severance and other postemployment benefits			$ 7.3
Severance and other cash benefits paid		$ 7.3