Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,503.4	$ 10,693.2	$ 11,176.3	$ 10,185.5
Other comprehensive income (loss) before reclassifications	(41.3)		(107.7)
Amounts reclassified from AOCL	(0.9)		66.8
Total Other Comprehensive Loss	(42.2)	(357.0)	(40.9)	(40.8)
Amount attributable to noncontrolling interests	(5.6)	(14.5)	(1.4)	(10.4)
Ending balance	11,726.6	10,810.0	11,726.6	10,810.0
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(49.5)		(37.6)
Other comprehensive income (loss) before reclassifications	7.5		(38.2)
Amounts reclassified from AOCL	(13.1)		20.7
Total Other Comprehensive Loss	(5.6)		(17.5)
Amount attributable to noncontrolling interests	0.1		0.1
Ending balance	(55.2)		(55.2)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,030.8)		(1,009.8)
Other comprehensive income (loss) before reclassifications	(48.8)		(65.6)
Amounts reclassified from AOCL	(2.6)		(2.6)
Total Other Comprehensive Loss	(51.4)		(68.2)
Amount attributable to noncontrolling interests	(5.7)		(1.5)
Ending balance	(1,076.5)		(1,076.5)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(664.5)		(694.5)
Other comprehensive income (loss) before reclassifications	0.0		(3.9)
Amounts reclassified from AOCL	14.8		48.7
Total Other Comprehensive Loss	14.8		44.8
Amount attributable to noncontrolling interests	0.0		0.0
Ending balance	(649.7)		(649.7)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,744.8)	(1,535.3)	(1,741.9)	(1,847.4)
Total Other Comprehensive Loss	(36.6)	(342.5)	(39.5)	(30.4)
Ending balance	$ (1,781.4)	$ (1,877.8)	$ (1,781.4)	$ (1,877.8)