Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Sales	$ 2,502.0	$ 2,216.3	$ 4,877.2	$ 4,471.0
Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 2,502.0	$ 2,216.3	$ 4,877.2	$ 4,471.0
Percent sales by supply mode	100.00%	100.00%	100.00%	100.00%
Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 1,056.1	$ 932.4	$ 1,989.1	$ 1,868.6
Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	584.6	492.7	1,147.6	991.4
Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	697.5	658.1	1,415.0	1,350.9
Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	97.9	79.3	202.4	171.9
Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	65.9	53.8	123.1	88.2
On-site | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 1,255.0	$ 1,102.1	$ 2,399.9	$ 2,226.3
Percent sales by supply mode	50.00%	50.00%	49.00%	50.00%
On-site | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 636.7	$ 516.2	$ 1,178.0	$ 1,050.7
On-site | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	202.3	160.3	391.0	331.7
On-site | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	416.0	425.6	830.9	843.9
On-site | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	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	0.0
Merchant | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 1,083.2	$ 981.1	$ 2,151.8	$ 1,984.6
Percent sales by supply mode	43.00%	44.00%	44.00%	44.00%
Merchant | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 419.4	$ 416.2	$ 811.1	$ 817.9
Merchant | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	382.3	332.4	756.6	659.7
Merchant | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	281.5	232.5	584.1	507.0
Merchant | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0	0.0
Merchant | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0	0.0
Sale of Equipment | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 163.8	$ 133.1	$ 325.5	$ 260.1
Percent sales by supply mode	7.00%	6.00%	7.00%	6.00%
Sale of Equipment | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 0.0	$ 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	0.0
Sale of Equipment | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	0.0	0.0	0.0	0.0
Sale of Equipment | Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	97.9	79.3	202.4	171.9
Sale of Equipment | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	$ 65.9	$ 53.8	$ 123.1	$ 88.2