Goodwill (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 845.1	$ 721.5	$ 845.1
Impairment loss			(145.3)
Acquisitions		78.0	3.5
Currency translation		(10.6)	18.2
Goodwill, net, ending balance		788.9	721.5
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	309.1	163.7	309.1
Impairment loss	(145.3)		(145.3)
Acquisitions		0.0	0.0
Currency translation		(1.6)	(0.1)
Goodwill, net, ending balance		162.1	163.7
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	380.6	402.4	380.6
Impairment loss			0.0
Acquisitions		29.5	3.5
Currency translation		(7.5)	18.3
Goodwill, net, ending balance		424.4	402.4
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	135.2	135.2	135.2
Impairment loss			0.0
Acquisitions		38.1	0.0
Currency translation		(1.4)	0.0
Goodwill, net, ending balance		171.9	135.2
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	20.2	20.2	20.2
Impairment loss			0.0
Acquisitions		0.0	0.0
Currency translation		(0.1)	0.0
Goodwill, net, ending balance		20.1	20.2
Corporate and other
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 0.0	0.0	0.0
Impairment loss			0.0
Acquisitions		10.4	0.0
Currency translation		0.0	0.0
Goodwill, net, ending balance		$ 10.4	$ 0.0

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.

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