Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,176.3	$ 10,185.5	$ 7,213.4
Other comprehensive loss before reclassifications	(726.5)	(19.3)	340.9
Amounts reclassified from AOCL	72.9	105.8	192.2
Total Other Comprehensive Income (Loss)	(653.6)	86.5	533.1
Spin-off of Versum			11.5
Amount attributable to noncontrolling interest	(19.9)	(19.0)	3.7
Ending balance	11,388.3	11,176.3	10,185.5
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(37.6)	(53.1)	(65.0)
Other comprehensive loss before reclassifications	(44.1)	45.9	(12.6)
Amounts reclassified from AOCL	12.3	(30.4)	24.2
Total Other Comprehensive Income (Loss)	(31.8)	15.5	11.6
Spin-off of Versum			0.2
Amount attributable to noncontrolling interest	(8.0)	0.0	(0.1)
Ending balance	(61.4)	(37.6)	(53.1)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,009.8)	(787.1)	(949.3)
Other comprehensive loss before reclassifications	(356.2)	(244.6)	101.9
Amounts reclassified from AOCL	(2.6)	3.1	57.3
Total Other Comprehensive Income (Loss)	(358.8)	(241.5)	159.2
Spin-off of Versum			6.0
Amount attributable to noncontrolling interest	(11.7)	(18.8)	3.0
Ending balance	(1,356.9)	(1,009.8)	(787.1)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(694.5)	(1,007.2)	(1,374.0)
Other comprehensive loss before reclassifications	(326.2)	179.4	251.6
Amounts reclassified from AOCL	63.2	133.1	110.7
Total Other Comprehensive Income (Loss)	(263.0)	312.5	362.3
Spin-off of Versum			5.3
Amount attributable to noncontrolling interest	(0.2)	(0.2)	0.8
Ending balance	(957.3)	(694.5)	(1,007.2)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,741.9)	(1,847.4)	(2,388.3)
Total Other Comprehensive Income (Loss)	(633.7)	105.5	529.4
Ending balance	$ (2,375.6)	$ (1,741.9)	$ (1,847.4)