Financial Instruments (Interest Rate Management Contracts and Cross Currency Interest Rate Swaps) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Jun. 30, 2025	Sep. 30, 2024
Interest Rate Swaps Contracts | Designated as hedging instrument | Fair Value Hedges
Derivative [Line Items]
US$ Notional	$ 800.0	$ 800.0
Average Pay %	Secured Overnight Financing Rate (SOFR) [Member]	Secured Overnight Financing Rate (SOFR) [Member]
Average Receive %	1.64%	1.64%
Years Average Maturity	2 years 2 months 12 days	3 years
Interest Rate Swaps Contracts | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 2,963.2	$ 2,159.3
Average Pay %	2.77%	2.72%
Average Receive %	SOFR	SOFR
Years Average Maturity	20 years 6 months	21 years 2 months 12 days
Interest Rate Swaps Contracts | Not designated as hedging instrument
Derivative [Line Items]
US$ Notional	$ 347.5	$ 461.4
Average Pay %	3.26%	3.27%
Average Receive %	SOFR	SOFR
Years Average Maturity	19 years 2 months 12 days	20 years 6 months
Cross currency interest rate swaps | Designated as hedging instrument | Net investment hedges
Derivative [Line Items]
US$ Notional	$ 0.0	$ 16.7
Average Pay %	0.00%	5.39%
Average Receive %	0.00%	3.64%
Years Average Maturity	0 years	2 months 12 days
Cross currency interest rate swaps | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 308.4	$ 410.6
Average Pay %	5.12%	4.96%
Average Receive %	3.01%	2.80%
Years Average Maturity	1 year 7 months 6 days	1 year 10 months 24 days
Cross currency interest rate swaps | Not designated as hedging instrument
Derivative [Line Items]
US$ Notional	$ 0.0	$ 34.7
Average Pay %	0.00%	5.39%
Average Receive %	0.00%	3.64%
Years Average Maturity	0 years	2 months 12 days