Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions		3 Months Ended																12 Months Ended
		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net																		$ (121.0)		$ (49.4)		$ (45.5)
Interest expense																		120.6		115.2		102.8
Business restructuring and cost reduction actions		$ 48.4	[1]	$ 42.7	[1]	$ 10.3	[1]	$ 50.0	[1]	$ 10.6	[1]	$ 13.2	[1]	$ 10.7	[1]	$ 0.0	[1]	151.4	[1]	34.5	[1]	180.1
Income (loss) from discontinued operations, net of tax																		(1,866.0)		460.5		(351.7)
Net income (loss) attributable to Air Products		$ (468.7)		$ (101.9)		$ (2,130.0)		$ (299.8)		$ (394.0)		$ (346.8)		$ 473.3		$ (363.6)		(3,000.4)		(631.1)		(1,277.9)
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																		18.3		0.2		0.6
Other income (expense), net																		5.1		(46.2)		16.9
Interest expense																		0.8		10.0		3.3
Net income (loss) attributable to Air Products																		24.2		(36.0)		20.8
Reclassification out of Accumulated Other Comprehensive Income | Currency Translation Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Business restructuring and cost reduction actions	[2]																	8.2		0.0		0.0
Income (loss) from discontinued operations, net of tax	[3]																	49.1		2.7		0.0
Net income (loss) attributable to Air Products																		57.3		2.7		0.0
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	[4]																	$ 110.7		$ 87.2		$ 97.0

[1] For additional information, see Note 5, Business Restructuring and Cost Reduction Actions.

[2] 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.

[3] 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.

[4] The components include items such as prior service cost amortization, actuarial loss amortization, and settlements and are reflected in net periodic benefit cost. Refer to Note 16, Retirement Benefits.