Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Sales		$ 2,216.3	$ 2,187.7	$ 4,471.0	$ 4,411.7
Operating Segments
Disaggregation of Revenue [Line Items]
Sales	[1]	$ 2,216.3	$ 2,187.7	$ 4,471.0	$ 4,411.7
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]	$ 932.4	$ 991.7	$ 1,868.6	$ 1,980.9
Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	[1]	492.7	494.4	991.4	1,018.6
Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	[1]	658.1	625.4	1,350.9	1,252.2
Industrial Gases - Global | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	[1]	79.3	53.8	171.9	122.0
Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales	[1]	53.8	22.4	88.2	38.0
On-site | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		$ 1,102.1	$ 1,145.5	$ 2,226.3	$ 2,344.7
Percent sales by supply mode		50.00%	52.00%	50.00%	53.00%
On-site | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		$ 516.2	$ 580.9	$ 1,050.7	$ 1,176.9
On-site | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		160.3	178.6	331.7	400.8
On-site | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		425.6	386.0	843.9	767.0
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		$ 981.1	$ 966.0	$ 1,984.6	$ 1,907.0
Percent sales by supply mode		44.00%	44.00%	44.00%	43.00%
Merchant | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		$ 416.2	$ 410.8	$ 817.9	$ 804.0
Merchant | Industrial Gases - EMEA | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		332.4	315.8	659.7	617.8
Merchant | Industrial Gases - Asia | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		232.5	239.4	507.0	485.2
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		$ 133.1	$ 76.2	$ 260.1	$ 160.0
Percent sales by supply mode		6.00%	4.00%	6.00%	4.00%
Sale of Equipment | Industrial Gases - Americas | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		$ 0.0	$ 0.0	$ 0.0	$ 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		79.3	53.8	171.9	122.0
Sale of Equipment | Corporate and other | Operating Segments
Disaggregation of Revenue [Line Items]
Sales		$ 53.8	$ 22.4	$ 88.2	$ 38.0

[1] The sales information noted above relates to external customers only. All intersegment sales are eliminated in consolidation. Intersegment sales are generally transacted at market pricing. We generally do not have intersegment sales from our regional industrial gases businesses. Equipment manufactured for our regional industrial gases segments are generally transferred at cost and are not reflect as an intersegment sale.