Financial Instruments (Interest Rate Management Contracts and Cross Currency Interest Rate Swaps) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2024	Sep. 30, 2023
Interest Rate Swaps Contracts | Designated as hedging instrument | Fair Value Hedges
Derivative [Line Items]
US$ Notional	$ 800.0	$ 800.0
Average Pay %	SOFR	SOFR
Average Receive %	1.64%	1.64%
Years Average Maturity	3 years 6 months	4 years
Interest Rate Swaps Contracts | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 1,740.3	$ 1,182.5
Average Pay %	2.82%	2.82%
Average Receive %	SOFR	SOFR
Years Average Maturity	21 years 7 months 6 days	22 years 1 month 6 days
Cross currency interest rate swaps | Designated as hedging instrument | Net investment hedges
Derivative [Line Items]
US$ Notional	$ 29.0	$ 80.8
Average Pay %	5.39%	4.60%
Average Receive %	3.64%	3.65%
Years Average Maturity	8 months 12 days	10 months 24 days
Cross currency interest rate swaps | Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
US$ Notional	$ 449.3	$ 598.2
Average Pay %	5.02%	4.89%
Average Receive %	2.82%	3.22%
Years Average Maturity	2 years 3 months 18 days	2 years 2 months 12 days
Cross currency interest rate swaps | Not designated as hedging instrument
Derivative [Line Items]
US$ Notional	$ 22.4	$ 44.5
Average Pay %	5.39%	5.39%
Average Receive %	3.64%	3.54%
Years Average Maturity	8 months 12 days	2 months 12 days