Acquisitions (Narrative) (Details) $ in Millions, ¥ in Billions					3 Months Ended					12 Months Ended
		May 01, 2019 USD ($)	Apr. 26, 2018 USD ($)	Apr. 26, 2018 CNY (¥)	Sep. 30, 2019 USD ($)		Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) acquisition		Sep. 30, 2018 USD ($) acquisition		Sep. 30, 2017 USD ($)	May 02, 2019	Apr. 26, 2018 CNY (¥)
Property, Plant and Equipment [Line Items]
Plant and equipment, net	[1]				$ 10,337.6					$ 10,337.6		$ 9,923.7		$ 8,440.2
Additions to plant and equipment										1,989.7		1,568.4		1,039.7
Equity issued related to asset acquisition												227.4
Long-term debt – related party					320.1	[2]				320.1	[2]	384.3	[2]			¥ 2.3
Business Acquisition [Line Items]
Gain on exchange of equity affiliate investments		$ 29.1			0.0		$ 29.1	$ 0.0	$ 0.0	29.1		0.0		$ 0.0
Business combinations, goodwill acquired during period										$ 48.6		$ 78.0
Joint Venture | Air Products Lu An Changzhi Co Ltd
Property, Plant and Equipment [Line Items]
Ownership interest by Air Products (percent)			60.00%													60.00%
Contribution of equipment to joint venture			$ 300.0
Additions to plant and equipment			235.0	¥ 1.5
Equity issued related to asset acquisition			227.0	1.4
Air Products Lu An Changzhi Co Ltd | Joint Venture
Property, Plant and Equipment [Line Items]
Consideration transferred in asset acquisition			1,200.0	¥ 7.9
Plant and equipment, net			$ 1,500.0
WuXi Hi-Tech Gas Co., Ltd.
Business Acquisition [Line Items]
Interest acquired in exchange transaction (percent)		50.00%
Ownership interest subsequent to acquisition date (percent)															100.00%
Gain from revaluation of previously held equity interest to acquisition date fair value		$ 15.0
Estimated acquisition date fair value of previously held equity interest		27.0
Business combinations, plant and equipment acquired during the period		28.0
Business combinations, recognized identifiable intangible assets		27.4
Business combinations, goodwill acquired during period		$ 3.9
Acquired finite-lived intangible assets, weighted-average useful life		10 years
Business combinations, tax deductible goodwill		$ 0.0
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Number of business combinations completed in period | acquisition										3		8
Business combinations, plant and equipment acquired during the period					75.1					$ 75.1
Business combinations, goodwill acquired during period										44.7
Business combinations, tax deductible goodwill					$ 1.7					1.7
Business combinations, aggregate purchase price, net of cash acquired										$ 126.6		$ 355.4
High-Tech Gases (Beijing) Co., Ltd.
Business Acquisition [Line Items]
Ownership interest percentage												50.00%			0.00%
Decrease in ownership interest in exchange transaction (percent)		50.00%
Gain from disposal of interest in equity method investment		$ 14.1
WuXi Hi-Tech Gas Co., Ltd.
Business Acquisition [Line Items]
Ownership interest percentage												50.00%
Interest acquired in exchange transaction (percent)		50.00%
Ownership interest subsequent to acquisition date (percent)															100.00%
Lu'An Loan To Joint Venture | Loans Payable
Property, Plant and Equipment [Line Items]
Loan to joint venture, face amount | ¥																¥ 2.6
Interest rate, stated percentage			5.50%													5.50%

[1] Long-lived assets include plant and equipment, net.

[2] Refer to Note 7, Acquisitions, for additional information regarding related party debt.