Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales	$ (10,323.0)	$ (8,856.3)	$ (8,918.9)
Cost of sales	(7,186.1)	(5,858.1)	(5,975.5)
Other income (expense), net	(52.8)	(65.4)	(49.3)
Interest expense	(141.8)	(109.3)	(137.0)
Other non-operating income (expense), net	(73.7)	(30.7)	(66.7)
Net income (loss) attributable to Air Products	(2,099.1)	(1,886.7)	(1,760.0)
Reclassification out of Accumulated Other Comprehensive Income | (Gain) Loss on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales	(0.6)	(0.2)
Cost of sales	(0.3)	(0.8)
Other income (expense), net	0.0	0.0
Interest expense	3.5	2.8
Other non-operating income (expense), net	40.9	(59.5)
Net income (loss) attributable to Air Products	43.5	(57.7)
Reclassification out of Accumulated Other Comprehensive Income | (Gain) Loss on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales			0.4
Cost of sales			0.2
Other income (expense), net			(3.0)
Interest expense			14.7
Other non-operating income (expense), net			0.0
Net income (loss) attributable to Air Products			12.3
Reclassification out of Accumulated Other Comprehensive Income | Currency Translation Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss) attributable to Air Products	0.0	0.0	(2.6)
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss) attributable to Air Products	$ 74.6	$ 82.5	$ 63.2