Goodwill (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 845.1	$ 845.1	$ 837.1
Impairment loss	(145.3)	(145.3)
Acquisitions		3.5
Currency translation		18.2	8.0
Goodwill, net, ending balance		721.5	845.1
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	309.1	309.1	297.6
Impairment loss		(145.3)
Acquisitions		0.0
Currency translation		(0.1)	11.5
Goodwill, net, ending balance		163.7	309.1
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	380.6	380.6	386.5
Impairment loss		0.0
Acquisitions		3.5
Currency translation		18.3	(5.9)
Goodwill, net, ending balance		402.4	380.6
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	135.2	135.2	133.1
Impairment loss		0.0
Acquisitions		0.0
Currency translation		0.0	2.1
Goodwill, net, ending balance		135.2	135.2
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 20.2	20.2	19.9
Impairment loss		0.0
Acquisitions		0.0
Currency translation		0.0	0.3
Goodwill, net, ending balance		$ 20.2	$ 20.2

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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