Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Sales	$ 10,323.0	$ 8,856.3	$ 8,918.9
Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 10,323.0	$ 8,856.3	$ 8,918.9
Percent sales by supply mode	100.00%	100.00%	100.00%
Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 4,167.6	$ 3,630.7	$ 3,873.5
Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	2,444.9	1,926.3	2,002.5
Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	2,920.8	2,716.5	2,663.6
Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	511.0	364.9	261.0
Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	278.7	217.9	118.3
On-site | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 5,061.4	$ 4,322.3	$ 4,581.6
Percent sales by supply mode	49.00%	49.00%	52.00%
On-site | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 2,469.5	$ 2,040.2	$ 2,230.6
On-site | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	873.1	629.3	728.4
On-site | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	1,718.8	1,652.8	1,622.6
On-site | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
On-site | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
Merchant | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 4,471.9	$ 3,951.2	$ 3,958.0
Percent sales by supply mode	43.00%	45.00%	44.00%
Merchant | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 1,698.1	$ 1,590.5	$ 1,642.9
Merchant | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	1,571.8	1,297.0	1,274.1
Merchant | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	1,202.0	1,063.7	1,041.0
Merchant | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
Merchant | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
Sale of Equipment | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 789.7	$ 582.8	$ 379.3
Percent sales by supply mode	8.00%	6.00%	4.00%
Sale of Equipment | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 0.0	$ 0.0	$ 0.0
Sale of Equipment | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
Sale of Equipment | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0
Sale of Equipment | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	511.0	364.9	261.0
Sale of Equipment | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 278.7	$ 217.9	$ 118.3