Accumulated Other Comprehensive Loss (Reclassification) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income/expense, net		$ (15.3)	$ (22.0)	$ (37.4)	$ (46.7)
Interest expense		30.4	30.5	60.2	60.0
Cost of sales		1,506.5	1,403.8	3,078.3	2,720.5
Income (loss) from discontinued operations, net of tax		0.0	(1,825.6)	1.0	(1,873.8)
Net Income (Loss) Attributable to Air Products		(416.4)	(2,130.0)	(571.0)	(2,429.8)
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		4.0	1.2	5.0	5.8
Other income/expense, net		(13.8)	5.5	(15.2)	26.6
Interest expense		2.3	(0.9)	3.5	(1.0)
Net Income (Loss) Attributable to Air Products		(7.5)	5.8	(6.7)	31.4
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		3.1
Income (loss) from discontinued operations, net of tax	[1]		49.1		49.1
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 (Loss) Attributable to Air Products	[2]	$ 26.6	$ 30.1	$ 49.5	$ 57.5

[1] The 2018 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 during the first quarter. The 2017 impact was reflected in "Income from discontinued operations, net of tax" and related to the sale of PMD during the second quarter.

[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.