Financial Instruments (Schedule of Outstanding Currency Price Risk Management Instruments) (Details) - Forward Exchange Contracts - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Derivative [Line Items]
US$ Notional	$ 4,313.3	$ 4,099.5
Years Average Maturity	11 months	10 months
Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
US$ Notional	$ 2,953.8	$ 3,150.2
Years Average Maturity	5 months	5 months
Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
US$ Notional	$ 369.5	$ 675.5
Years Average Maturity	2 years 6 months	3 years
Not Designated as Hedging Instrument
Derivative [Line Items]
US$ Notional	$ 990.0	$ 273.8
Years Average Maturity	1 year 8 months	1 month