Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Sales	$ 2,320.1	$ 2,065.2	$ 2,216.3	$ 2,254.7	$ 2,283.2	$ 2,224.0	$ 2,187.7	$ 2,224.0	$ 8,856.3	$ 8,918.9	$ 8,930.2
Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 8,856.3	$ 8,918.9	8,930.2
Percent sales by supply mode									100.00%	100.00%
Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 3,630.7	$ 3,873.5	3,758.8
Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									1,926.3	2,002.5	2,193.3
Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									2,716.5	2,663.6	2,458.0
Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									364.9	261.0	436.1
Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									217.9	118.3	$ 84.0
On-site | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 4,322.3	$ 4,581.6
Percent sales by supply mode									49.00%	52.00%
On-site | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 2,040.2	$ 2,230.6
On-site | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									629.3	728.4
On-site | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									1,652.8	1,622.6
On-site | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
On-site | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
Merchant | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 3,951.2	$ 3,958.0
Percent sales by supply mode									45.00%	44.00%
Merchant | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 1,590.5	$ 1,642.9
Merchant | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									1,297.0	1,274.1
Merchant | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									1,063.7	1,041.0
Merchant | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
Merchant | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
Sale of Equipment | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 582.8	$ 379.3
Percent sales by supply mode									6.00%	4.00%
Sale of Equipment | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 0.0	$ 0.0
Sale of Equipment | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
Sale of Equipment | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									0.0	0.0
Sale of Equipment | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									364.9	261.0
Sale of Equipment | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales									$ 217.9	$ 118.3