Financial Instruments (Currency Price Risk Management Instruments) (Details) - Forward exchange contracts - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Derivative [Line Items]
US$ Notional	$ 4,417.1	$ 5,163.9
Years Average Maturity	9 months 18 days	9 months 18 days
Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
US$ Notional	$ 2,985.0	$ 2,842.1
Years Average Maturity	4 months 24 days	6 months
Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
US$ Notional	$ 656.4	$ 636.6
Years Average Maturity	3 years 3 months 18 days	3 years 9 months 18 days
Not Designated as Hedging Instrument
Derivative [Line Items]
US$ Notional	$ 775.7	$ 1,685.2
Years Average Maturity	2 months 12 days	3 months 18 days