Goodwill (Schedule of Goodwill by Segment) (Details) $ in Millions	6 Months Ended
Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 721.5
Acquisitions	62.9
Currency translation	30.6
Goodwill, net, ending balance	815.0
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	163.7
Acquisitions	0.0
Currency translation	3.5
Goodwill, net, ending balance	167.2
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	402.4
Acquisitions	27.7
Currency translation	22.0
Goodwill, net, ending balance	452.1
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	135.2
Acquisitions	35.2
Currency translation	5.0
Goodwill, net, ending balance	175.4
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	20.2
Acquisitions	0.0
Currency translation	0.1
Goodwill, net, ending balance	$ 20.3

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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