Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions		3 Months Ended												12 Months Ended
		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net														$ (50.2)	$ (121.0)		$ (49.4)
Interest expense														130.5	120.6		115.2
Cost of sales														6,189.5	5,751.5		5,177.3
Cost reduction and asset actions						$ 48.4	[1]	$ 42.7	[1]	$ 10.3	[1]	$ 50.0	[1]	0.0	151.4	[1]	34.5
Loss from discontinued operations, net of tax														(42.2)	(1,866.0)		460.5
Net income (loss) attributable to Air Products		$ (452.9)	$ (473.9)	$ (416.4)	$ (154.6)	$ (468.7)		$ (101.9)		$ (2,130.0)		$ (299.8)		(1,497.8)	(3,000.4)		(631.1)
Reclassification out of Accumulated Other Comprehensive Income | (Gain) Loss on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales/cost of sales														7.1	18.3		0.2
Other income (expense), net														(42.6)	5.1		(46.2)
Interest expense														5.1	0.8		10.0
Net income (loss) attributable to Air Products														(30.4)	24.2		(36.0)
Reclassification out of Accumulated Other Comprehensive Income | Currency Translation Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[2]													3.1	0.0		0.0
Cost reduction and asset actions	[3]													0.0	8.2		0.0
Loss from discontinued operations, net of tax	[4]													0.0	49.1		2.7
Net income (loss) attributable to Air Products														3.1	57.3		2.7
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	[5]													$ 133.1	$ 110.7		$ 87.2

[1] For additional information, refer to Note 5, Cost Reduction and Asset Actions.

[2] The fiscal year 2018 impact relates to an equipment sale resulting from the termination of a contract in the Industrial Gases – Asia segment during the first quarter.

[3] The fiscal year 2017 impact relates to the planned sale of a non-industrial gas hardgoods business in the Industrial Gases – Americas segment recorded in the third quarter.

[4] The fiscal year 2017 impact relates to the sale of PMD during the second quarter. The fiscal year 2016 impact primarily relates to the sale of an equity affiliate in the first quarter.

[5] The components of net periodic benefit cost reclassified out of AOCL include items such as prior service cost amortization, actuarial loss amortization, and settlements and are included in “Other non-operating income (expense), net” on the consolidated income statements. Refer to Note 16, Retirement Benefits, for additional information.