Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income/expense, net		$ (10.4)	$ (15.3)	$ (19.0)	$ (37.4)
Interest expense		35.4	30.4	72.7	60.2
Cost of sales		1,474.7	1,506.5	3,018.7	3,078.3
Net Income Attributable to Air Products		(421.3)	(416.4)	(768.8)	(571.0)
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		(0.1)	4.0	0.4	5.0
Other income/expense, net		33.2	(13.8)	25.8	(15.2)
Interest expense		3.8	2.3	7.6	3.5
Net Income Attributable to Air Products		36.9	(7.5)	33.8	(6.7)
Reclassification out of Accumulated Other Comprehensive Income | Currency Translation Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[1]	0.0	0.0	0.0	3.1
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 Attributable to Air Products	[2]	$ 18.7	$ 26.6	$ 33.9	$ 49.5

[1] The fiscal year 2018 impact is reflected in "Cost of sales" on the consolidated income statements and relates to an equipment sale resulting from the termination of a contract in the Industrial Gases – Asia segment during the first quarter.

[2] 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 9, Retirement Benefits, for additional information.