Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,388.3	$ 11,176.3	$ 10,185.5
Other comprehensive income (loss) before reclassifications	208.7	(726.5)	(19.3)
Amounts reclassified from AOCL	24.8	72.9	105.8
Total Other Comprehensive Income (Loss)	233.5	(653.6)	86.5
Amount attributable to noncontrolling interest	(2.0)	(19.9)	(19.0)
Ending balance	12,443.1	11,388.3	11,176.3
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(61.4)	(37.6)	(53.1)
Other comprehensive income (loss) before reclassifications		(44.1)	45.9
Amounts reclassified from AOCL		12.3	(30.4)
Total Other Comprehensive Income (Loss)		(31.8)	15.5
Amount attributable to noncontrolling interest		(8.0)	0.0
Ending balance		(61.4)	(37.6)
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	43.5
Amounts reclassified from AOCL	(57.7)
Total Other Comprehensive Income (Loss)	(14.2)
Amount attributable to noncontrolling interest	(21.1)
Ending balance	(54.5)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,356.9)	(1,009.8)	(787.1)
Other comprehensive income (loss) before reclassifications	233.4	(356.2)	(244.6)
Amounts reclassified from AOCL	0.0	(2.6)	3.1
Total Other Comprehensive Income (Loss)	233.4	(358.8)	(241.5)
Amount attributable to noncontrolling interest	19.3	(11.7)	(18.8)
Ending balance	(1,142.8)	(1,356.9)	(1,009.8)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(957.3)	(694.5)	(1,007.2)
Other comprehensive income (loss) before reclassifications	(68.2)	(326.2)	179.4
Amounts reclassified from AOCL	82.5	63.2	133.1
Total Other Comprehensive Income (Loss)	14.3	(263.0)	312.5
Amount attributable to noncontrolling interest	(0.2)	(0.2)	(0.2)
Ending balance	(942.8)	(957.3)	(694.5)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,375.6)	(1,741.9)	(1,847.4)
Total Other Comprehensive Income (Loss)	235.5	(633.7)	105.5
Ending balance	$ (2,140.1)	$ (2,375.6)	$ (1,741.9)