Financial Instruments (Interest Rate Management Contracts and Cross Currency Interest Rate Swaps) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Interest Rate Swaps Contracts | Designated as Hedging Instrument | Fair Value Hedges
Derivative [Line Items]
US$ Notional	$ 200.0	$ 200.0
Average Pay %	LIBOR	LIBOR
Average Receive %	2.76%	2.76%
Years Average Maturity	1 year 7 months 6 days	2 years 1 month 6 days
Cross Currency Interest Rate Swaps | Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
US$ Notional	$ 222.9	$ 216.8
Average Pay %	4.74%	4.80%
Average Receive %	3.32%	3.31%
Years Average Maturity	3 years	3 years 6 months
Cross Currency Interest Rate Swaps | Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
US$ Notional	$ 1,063.6	$ 1,129.3
Average Pay %	4.83%	4.92%
Average Receive %	3.07%	3.04%
Years Average Maturity	2 years	2 years 3 months 18 days
Cross Currency Interest Rate Swaps | Not Designated as Hedging Instrument
Derivative [Line Items]
US$ Notional	$ 0.0	$ 6.1
Average Pay %	0.00%	2.55%
Average Receive %	0.00%	3.72%
Years Average Maturity	0 years	4 years 6 months