Goodwill (Schedule of Goodwill by Segment) (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 797.1
Currency translation and other	(11.8)
Goodwill, net, ending balance	785.3
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	156.3
Currency translation and other	(7.8)
Goodwill, net, ending balance	148.5
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	432.3
Currency translation and other	(2.0)
Goodwill, net, ending balance	430.3
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	178.5
Currency translation and other	(1.5)
Goodwill, net, ending balance	177.0
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	19.6
Currency translation and other	(0.5)
Goodwill, net, ending balance	19.1
Corporate and other
Goodwill [Roll Forward]
Goodwill, net, beginning balance	10.4
Currency translation and other	0.0
Goodwill, net, ending balance	$ 10.4