Financial Instruments (Schedule of Outstanding Currency Price Risk Management Instruments) (Details) - Forward Exchange Contracts - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Derivative [Line Items]
US$ Notional	$ 4,273.2	$ 4,099.5
Years Average Maturity	10 months	10 months
Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
US$ Notional	$ 3,209.0	$ 3,150.2
Years Average Maturity	6 months	5 months
Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
US$ Notional	$ 674.0	$ 675.5
Years Average Maturity	2 years 10 months	3 years
Not Designated as Hedging Instrument
Derivative [Line Items]
US$ Notional	$ 390.2	$ 273.8
Years Average Maturity	2 months	1 month