Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,388.3	$ 11,176.3
Other comprehensive income before reclassifications	286.1
Amounts reclassified from AOCL	16.1
Total Other Comprehensive Income (Loss)	302.2	(70.2)
Amount attributable to noncontrolling interests	15.2	(0.9)
Ending balance	11,929.8	11,203.4
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(61.4)
Other comprehensive income before reclassifications	22.1
Amounts reclassified from AOCL	(3.6)
Total Other Comprehensive Income (Loss)	18.5
Amount attributable to noncontrolling interests	5.6
Ending balance	(48.5)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,356.9)
Other comprehensive income before reclassifications	264.0
Amounts reclassified from AOCL	0.0
Total Other Comprehensive Income (Loss)	264.0
Amount attributable to noncontrolling interests	9.6
Ending balance	(1,102.5)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(957.3)
Other comprehensive income before reclassifications	0.0
Amounts reclassified from AOCL	19.7
Total Other Comprehensive Income (Loss)	19.7
Amount attributable to noncontrolling interests	0.0
Ending balance	(937.6)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,375.6)	(1,741.9)
Total Other Comprehensive Income (Loss)	287.0	(69.3)
Ending balance	$ (2,088.6)	$ (1,811.2)