Financial Instruments (Interest Rate Management Contracts and Cross Currency Interest Rate Swaps) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2026	Sep. 30, 2025
Interest Rate Swaps Contracts | Designated as hedging instrument | Fair Value Hedges
Derivative [Line Items]
US$ Notional	$ 600.0	$ 800.0
Average Pay %	Secured Overnight Financing Rate (SOFR) [Member]	Secured Overnight Financing Rate (SOFR) [Member]
Average Receive %	1.80%	1.64%
Years Average Maturity	2 years 1 month 6 days	2 years
Interest Rate Swaps Contracts | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 3,563.1	$ 3,106.0
Average Pay %	2.82%	2.78%
Average Receive %	SOFR	SOFR
Years Average Maturity	19 years 7 months 6 days	20 years 1 month 6 days
Interest Rate Swaps Contracts | Not designated as hedging instrument
Derivative [Line Items]
US$ Notional	$ 0.0	$ 269.1
Average Pay %	0.00%	3.28%
Average Receive %	SOFR	SOFR
Years Average Maturity	0 years	20 years 2 months 12 days
Cross currency interest rate swaps(A) | Designated as hedging instrument | Net investment hedges
Derivative [Line Items]
US$ Notional	$ 2,054.9	$ 70.3
Average Pay %	2.08%	4.86%
Average Receive %	3.70%	4.53%
Years Average Maturity	2 years 1 month 6 days	6 months
Cross currency interest rate swaps(A) | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 84.2	$ 247.7
Average Pay %	4.70%	5.21%
Average Receive %	2.88%	3.12%
Years Average Maturity	10 months 24 days	1 year 7 months 6 days
Cross currency interest rate swaps(A) | Not designated as hedging instrument
Derivative [Line Items]
US$ Notional	$ 15.4	$ 0.0
Average Pay %	0.15%	0.00%
Average Receive %	1.85%	0.00%
Years Average Maturity	1 year 1 month 6 days	0 years