Business Segment Information (Schedule of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Segment Reporting Information [Line Items]
Sales	$ 2,375.2	$ 2,254.7
Operating income (loss)	539.1	561.0
Depreciation and amortization	323.7	289.2
Equity affiliates' income	69.3	58.2
Total assets	26,088.1		$ 25,168.5
Operating Segments
Segment Reporting Information [Line Items]
Sales	2,375.2	2,254.7
Operating income (loss)	539.1	561.0
Depreciation and amortization	323.7	289.2
Equity affiliates' income	69.3	58.2
Total assets	26,088.1		25,168.5
Industrial Gases - Americas | Operating Segments
Segment Reporting Information [Line Items]
Sales	933.0	936.2
Operating income (loss)	225.8	257.2
Depreciation and amortization	151.8	131.8
Equity affiliates' income	22.3	20.6
Total assets	6,749.8		6,610.1
Industrial Gases - EMEA | Operating Segments
Segment Reporting Information [Line Items]
Sales	563.0	498.7
Operating income (loss)	141.5	120.5
Depreciation and amortization	55.4	48.4
Equity affiliates' income	25.0	19.3
Total assets	4,249.2		3,917.0
Industrial Gases - Asia | Operating Segments
Segment Reporting Information [Line Items]
Sales	717.5	692.8
Operating income (loss)	214.8	228.5
Depreciation and amortization	107.9	101.6
Equity affiliates' income	19.9	16.9
Total assets	7,274.7		6,842.9
Industrial Gases - Global | Operating Segments
Segment Reporting Information [Line Items]
Sales	104.5	92.6
Operating income (loss)	(4.6)	3.6
Depreciation and amortization	2.6	2.4
Equity affiliates' income	2.1	1.4
Total assets	485.3		397.8
Corporate and other | Operating Segments
Segment Reporting Information [Line Items]
Sales	57.2	34.4
Operating income (loss)	(38.4)	(48.8)
Depreciation and amortization	6.0	5.0
Equity affiliates' income	0.0	$ 0.0
Total assets	$ 7,329.1		$ 7,400.7