Consolidated Comprehensive Income Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 3,021.2	$ 661.5	$ 1,317.6
Other Comprehensive Income (Loss), net of tax:
Translation adjustments, net of tax of ($19.3), ($19.8), and $45.2	101.9	9.9	(699.3)
Net gain (loss) on derivatives, net of tax of ($11.0), $9.1, and ($16.0)	(12.6)	13.7	(35.0)
Pension and postretirement benefits, net of tax of $109.0, ($157.4), and ($148.5)	251.6	(335.1)	(278.5)
Reclassification adjustments:
Currency translation adjustment	57.3	2.7	0.0
Derivatives, net of tax of $11.7, ($9.4), and $7.0	24.2	(36.0)	20.8
Pension and postretirement benefits, net of tax of $50.7, $43.0, and $47.7	110.7	87.2	97.0
Total Other Comprehensive Income (Loss)	533.1	(257.6)	(895.0)
Comprehensive Income	3,554.3	403.9	422.6
Net Income Attributable to Noncontrolling Interests	20.8	30.4	39.7
Other Comprehensive Income (Loss) Attributable to Noncontrolling Interests	3.7	4.8	(11.0)
Comprehensive Income Attributable to Air Products	$ 3,529.8	$ 368.7	$ 393.9