Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	35.00%	35.00%	35.00%
Foreign statutory tax rate, minimum (as percent)	17.00%
Income Tax Holiday [Line Items]
Federal foreign tax credit carryforward	$ 65.8
Federal foreign tax credit carryforward, windfall benefit	4.8
Federal research credit carryforward	3.3
Tax credit carryforwards	64.2	$ 49.6
Foreign loss carryforwards subject to expiration	26.8
Decrease in valuation allowance	22.1
Cumulative undistributed earnings	683.0
U.S. income and foreign withholding taxes estimate	155.0
Unrecognized tax benefits	12.9	10.3	$ 16.0	$ 21.6
Unrecognized tax benefits that would impact effective tax rate	$ 12.6	10.0
Foreign Tax Authority
Income Tax Holiday [Line Items]
Income tax holiday period	7 years
Tax benefit of holidays, reduction	50.00%
Net benefit of tax holidays	$ 7.1	9.6	4.9
Loss carryforwards	46.3
Foreign Tax Authority | Air Products
Income Tax Holiday [Line Items]
Income tax payments	9.6	$ 14.3	$ 7.2
State
Income Tax Holiday [Line Items]
Loss carryforwards	$ 85.6