Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net		$ (22.1)	$ (24.7)
Interest expense		29.8	29.5
Net Income (Loss) Attributable to Air Products		(154.6)	(299.8)
Reclassification out of Accumulated Other Comprehensive Income | (Gain) Loss on Cash Flow Hedges, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales/Cost of sales		1.0	4.6
Other income (expense), net		(1.4)	21.1
Interest expense		1.2	(0.1)
Net Income (Loss) Attributable to Air Products		0.8	25.6
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	[1]	3.1	0.0
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefits, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss) Attributable to Air Products	[2]	$ 22.9	$ 27.4

[1] The impact is reflected in "Cost of sales" and relates to an equipment sale resulting from the termination of a contract in the Industrial Gases – Asia segment.

[2] The components of net periodic benefit cost reclassified out of accumulated other comprehensive loss 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 11, Retirement Benefits, for additional information.