Goodwill (Schedule of Goodwill by Segment) (Details) $ in Millions	9 Months Ended
	Jun. 30, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 797.1
Currency translation and other	2.2
Goodwill, net, ending balance	799.3
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	156.3
Currency translation and other	(6.0)
Goodwill, net, ending balance	150.3
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	432.3
Currency translation and other	8.7
Goodwill, net, ending balance	441.0
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	178.5
Currency translation and other	(0.3)
Goodwill, net, ending balance	178.2
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	19.6
Currency translation and other	(0.2)
Goodwill, net, ending balance	19.4
Corporate and other
Goodwill [Roll Forward]
Goodwill, net, beginning balance	10.4
Currency translation and other	0.0
Goodwill, net, ending balance	$ 10.4