Share-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from option exercises	$ 1.1	$ 7.9	$ 24.0
Total tax benefit realized from stock option exercises	2.5
Excess tax benefit from stock option exercises	$ 1.9
Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	900,000
Deferred Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units/shares granted	239,000
Weighted-average grant date fair value (in dollars per share)	$ 385.22
Cash payments made for deferred stock units	$ 4.6	2.7	3.6
Unrecognized compensation costs	$ 68.5
Unrecognized compensation costs, period for recognition, years	1 year 8 months 12 days
Fair value of deferred stock units paid	$ 94.5	$ 24.1	$ 45.3
Deferred Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting or deferral period	2 years
Deferred Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting or deferral period	5 years
Director Deferred Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period after service in which to elect payment	10 years
Market-Based Deferred Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting or deferral period	3 years
Number of units/shares granted	95,490	102,120	85,612
Weighted-average grant date fair value (in dollars per share)	$ 470.13	$ 302.10	$ 502.03
Time-Based Deferred Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units/shares granted	143,059	146,947	119,954
Weighted-average grant date fair value (in dollars per share)	$ 328.54	$ 270.86	$ 308.91
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregated intrinsic value, outstanding	$ 0.0
Aggregated intrinsic value, exercisable	0.0
Intrinsic value of stock options exercised	10.5	$ 35.1	$ 53.5
Cash received from option exercises	$ 1.1