Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,176.3	$ 10,185.5
Other comprehensive loss before reclassifications	(82.3)
Amounts reclassified from AOCL	12.1
Total Other Comprehensive Income (Loss)	(70.2)	153.7
Amount attributable to noncontrolling interests	(0.9)	1.9
Ending balance	11,203.4	10,321.2
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(37.6)
Other comprehensive loss before reclassifications	(10.3)
Amounts reclassified from AOCL	(3.1)
Total Other Comprehensive Income (Loss)	(13.4)
Amount attributable to noncontrolling interests	(0.1)
Ending balance	(50.9)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,009.8)
Other comprehensive loss before reclassifications	(68.1)
Amounts reclassified from AOCL	0.0
Total Other Comprehensive Income (Loss)	(68.1)
Amount attributable to noncontrolling interests	(0.8)
Ending balance	(1,077.1)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(694.5)
Other comprehensive loss before reclassifications	(3.9)
Amounts reclassified from AOCL	15.2
Total Other Comprehensive Income (Loss)	11.3
Amount attributable to noncontrolling interests	0.0
Ending balance	(683.2)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,741.9)	(1,847.4)
Total Other Comprehensive Income (Loss)	(69.3)	151.8
Ending balance	$ (1,811.2)	$ (1,695.6)