Business Segment Information (Schedule of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Sales	$ 2,155.7	$ 1,980.1	$ 4,372.3	$ 3,862.6
Operating income (loss)	455.4	395.6	916.1	723.9
Depreciation and amortization			467.9	417.9
Equity affiliates' income	43.7	34.2	57.5	72.2
Total assets	18,511.1		18,511.1		$ 18,467.2
Operating Segments
Segment Reporting Information [Line Items]
Sales	2,155.7	1,980.1	4,372.3	3,862.6
Operating income (loss)	455.4	405.9	916.1	816.7
Depreciation and amortization	240.0	211.8	467.9	417.9
Equity affiliates' income	43.7	34.2	90.0	72.2
Total assets	18,511.1		18,511.1		18,457.0
Industrial Gases - Americas | Operating Segments
Segment Reporting Information [Line Items]
Sales	913.2	890.1	1,823.0	1,754.0
Operating income (loss)	222.3	223.2	439.5	446.5
Depreciation and amortization	122.3	116.0	240.1	227.8
Equity affiliates' income	16.9	13.0	35.5	27.7
Total assets	5,915.0		5,915.0		5,840.8
Industrial Gases - EMEA | Operating Segments
Segment Reporting Information [Line Items]
Sales	561.6	414.2	1,077.5	813.9
Operating income (loss)	116.7	88.6	221.2	178.6
Depreciation and amortization	50.7	41.6	99.8	83.8
Equity affiliates' income	11.1	8.3	24.2	17.8
Total assets	3,475.5		3,475.5		3,276.1
Industrial Gases - Asia | Operating Segments
Segment Reporting Information [Line Items]
Sales	557.6	435.9	1,201.2	874.2
Operating income (loss)	148.7	112.3	324.2	230.7
Depreciation and amortization	62.6	49.3	119.4	96.0
Equity affiliates' income	15.4	12.9	29.6	26.4
Total assets	4,779.1		4,779.1		4,412.1
Industrial Gases - Global | Operating Segments
Segment Reporting Information [Line Items]
Sales	101.7	216.5	234.7	364.4
Operating income (loss)	12.1	22.7	21.6	30.9
Depreciation and amortization	1.9	1.7	3.5	3.7
Equity affiliates' income	0.3	0.0	0.7	0.3
Total assets	252.5		252.5		279.6
Corporate and other | Operating Segments
Segment Reporting Information [Line Items]
Sales	21.6	23.4	35.9	56.1
Operating income (loss)	(44.4)	(40.9)	(90.4)	(70.0)
Depreciation and amortization	2.5	3.2	5.1	6.6
Equity affiliates' income	0.0	$ 0.0	0.0	$ 0.0
Total assets	$ 4,089.0		$ 4,089.0		$ 4,648.4