Financial Instruments (Currency Price Risk Management Instruments) (Details) - Forward Exchange Contracts - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Derivative [Line Items]
US$ Notional	$ 4,475.2	$ 4,302.5
Years Average Maturity	7 months 6 days	7 months 6 days
Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
US$ Notional	$ 2,682.9	$ 2,418.2
Years Average Maturity	4 months 24 days	6 months
Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
US$ Notional	$ 450.0	$ 830.8
Years Average Maturity	1 year 7 months 6 days	10 months 24 days
Not Designated as Hedging Instrument
Derivative [Line Items]
US$ Notional	$ 1,342.3	$ 1,053.5
Years Average Maturity	6 months	7 months 6 days