Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 12,443.1	$ 11,388.3	$ 11,176.3
Other comprehensive income (loss) before reclassifications	544.9	208.7	(726.5)
Amounts reclassified from AOCL	118.1	24.8	72.9
Total Other Comprehensive Income (Loss)	663.0	233.5	(653.6)
Amount attributable to noncontrolling interest	38.8	(2.0)	(19.9)
Ending balance	14,088.0	12,443.1	11,388.3
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(61.4)	(37.6)
Other comprehensive income (loss) before reclassifications			(44.1)
Amounts reclassified from AOCL			12.3
Total Other Comprehensive Income (Loss)			(31.8)
Amount attributable to noncontrolling interest			(8.0)
Ending balance			(61.4)
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(54.5)
Other comprehensive income (loss) before reclassifications	3.3	43.5
Amounts reclassified from AOCL	43.5	(57.7)
Total Other Comprehensive Income (Loss)	46.8	(14.2)
Amount attributable to noncontrolling interest	20.6	(21.1)
Ending balance	(28.3)	(54.5)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,142.8)	(1,356.9)	(1,009.8)
Other comprehensive income (loss) before reclassifications	267.3	233.4	(356.2)
Amounts reclassified from AOCL	0.0	0.0	(2.6)
Total Other Comprehensive Income (Loss)	267.3	233.4	(358.8)
Amount attributable to noncontrolling interest	18.3	19.3	(11.7)
Ending balance	(893.8)	(1,142.8)	(1,356.9)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(942.8)	(957.3)	(694.5)
Other comprehensive income (loss) before reclassifications	274.3	(68.2)	(326.2)
Amounts reclassified from AOCL	74.6	82.5	63.2
Total Other Comprehensive Income (Loss)	348.9	14.3	(263.0)
Amount attributable to noncontrolling interest	(0.1)	(0.2)	(0.2)
Ending balance	(593.8)	(942.8)	(957.3)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,140.1)	(2,375.6)	(1,741.9)
Total Other Comprehensive Income (Loss)	624.2	235.5	(633.7)
Ending balance	$ (1,515.9)	$ (2,140.1)	$ (2,375.6)