Business Segment Information (Schedule of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Segment Reporting Information [Line Items]
Sales	$ 2,216.6	$ 1,882.5
Operating income (loss)	460.7	328.3
Depreciation and amortization	227.9	206.1
Equity affiliates' income	13.8	38.0
Total assets	18,208.8		$ 18,467.2
Operating Segments
Segment Reporting Information [Line Items]
Sales	2,216.6	1,882.5
Operating income (loss)	460.7	410.8
Depreciation and amortization	227.9	206.1
Equity affiliates' income	46.3	38.0
Total assets	18,198.6		18,457.0
Industrial Gases - Americas | Operating Segments
Segment Reporting Information [Line Items]
Sales	909.8	863.9
Operating income (loss)	217.2	223.3
Depreciation and amortization	117.8	111.8
Equity affiliates' income	18.6	14.7
Total assets	5,878.6		5,840.8
Industrial Gases - EMEA | Operating Segments
Segment Reporting Information [Line Items]
Sales	515.9	399.7
Operating income (loss)	104.5	90.0
Depreciation and amortization	49.1	42.2
Equity affiliates' income	13.1	9.5
Total assets	3,378.5		3,276.1
Industrial Gases - Asia | Operating Segments
Segment Reporting Information [Line Items]
Sales	643.6	438.3
Operating income (loss)	175.5	118.4
Depreciation and amortization	56.8	46.7
Equity affiliates' income	14.2	13.5
Total assets	4,592.3		4,412.1
Industrial Gases - Global | Operating Segments
Segment Reporting Information [Line Items]
Sales	133.0	147.9
Operating income (loss)	9.5	8.2
Depreciation and amortization	1.6	2.0
Equity affiliates' income	0.4	0.3
Total assets	285.5		279.6
Corporate and other | Operating Segments
Segment Reporting Information [Line Items]
Sales	14.3	32.7
Operating income (loss)	(46.0)	(29.1)
Depreciation and amortization	2.6	3.4
Equity affiliates' income	0.0	$ 0.0
Total assets	$ 4,063.7		$ 4,648.4