Business Segment and Geographic Information (Schedule of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Segment Reporting Information [Line Items]
Sales	$ 2,203.1		$ 2,121.9		$ 1,980.1		$ 1,882.5		$ 1,945.5		$ 1,914.5		$ 1,777.4		$ 1,866.3		$ 8,187.6		$ 7,503.7		$ 7,824.3
Operating income (loss)	455.7	[1]	252.6	[1]	391.2	[1]	328.1	[1]	391.0	[1]	394.6	[1]	371.6	[1]	372.5	[1]	1,427.6	[1]	1,529.7	[1]	1,233.2
Depreciation and amortization																	865.8		854.6		858.5
Equity affiliates' income (loss)	44.8		$ (36.9)	[2]	$ 34.2		$ 38.0		39.3		$ 42.1		$ 32.3		$ 33.3		80.1	[2]	147.0		152.3
Expenditures for long-lived assets																	1,039.7		907.7		1,162.4
Investment in net assets of and advances to equity affiliates	1,286.9								1,283.6								1,286.9		1,283.6
Total assets	18,467.2								18,028.6								18,467.2		18,028.6		17,316.6
Operating Segments
Segment Reporting Information [Line Items]
Sales																	8,187.6		7,503.7		7,824.3
Operating income (loss)																	1,769.6		1,619.9		1,388.6
Depreciation and amortization																	865.8		854.6		858.5
Equity affiliates' income (loss)																	159.6		147.0		152.3
Expenditures for long-lived assets																	1,039.7		907.7		1,162.4
Investment in net assets of and advances to equity affiliates	1,286.9								1,283.6								1,286.9		1,283.6		1,249.8
Total assets	18,457.0								16,060.1								18,457.0		16,060.1		14,760.0
Industrial Gases - Americas | Operating Segments
Segment Reporting Information [Line Items]
Sales																	3,637.0		3,344.1		3,694.5
Operating income (loss)																	950.6		893.2		806.1
Depreciation and amortization																	464.4		443.6		417.5
Equity affiliates' income (loss)																	58.1		52.7		64.6
Expenditures for long-lived assets																	427.2		406.6		414.5
Investment in net assets of and advances to equity affiliates	287.5								250.6								287.5		250.6		249.7
Total assets	5,840.8								5,896.7								5,840.8		5,896.7		5,782.5
Industrial Gases - EMEA | Operating Segments
Segment Reporting Information [Line Items]
Sales																	1,780.4		1,704.4		1,866.4
Operating income (loss)																	387.1		384.6		331.3
Depreciation and amortization																	177.1		185.7		194.3
Equity affiliates' income (loss)																	47.1		36.5		42.4
Expenditures for long-lived assets																	143.2		159.5		215.6
Investment in net assets of and advances to equity affiliates	508.6								580.5								508.6		580.5		564.1
Total assets	3,276.1								3,178.6								3,276.1		3,178.6		3,324.1
Industrial Gases - Asia | Operating Segments
Segment Reporting Information [Line Items]
Sales																	1,964.7		1,720.4		1,661.3
Operating income (loss)																	531.2		451.0		389.3
Depreciation and amortization																	203.2		197.9		209.9
Equity affiliates' income (loss)																	53.5		57.8		46.1
Expenditures for long-lived assets																	337.8		313.3		402.5
Investment in net assets of and advances to equity affiliates	471.8								442.5								471.8		442.5		421.7
Total assets	4,412.1								4,232.7								4,412.1		4,232.7		4,159.1
Industrial Gases - Global | Operating Segments
Segment Reporting Information [Line Items]
Sales																	722.9		498.8		286.7
Operating income (loss)																	71.3		(21.3)		(51.6)
Depreciation and amortization																	8.9		7.9		16.5
Equity affiliates' income (loss)																	0.9		0.0		(0.8)
Expenditures for long-lived assets																	25.6		6.0		94.8
Investment in net assets of and advances to equity affiliates	19.0								10.0								19.0		10.0		14.3
Total assets	279.6								367.6								279.6		367.6		370.5
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Sales																	82.6		236.0		315.4
Operating income (loss)																	(170.6)		(87.6)		(86.5)
Depreciation and amortization																	12.2		19.5		20.3
Equity affiliates' income (loss)																	0.0		0.0		0.0
Expenditures for long-lived assets																	105.9		22.3		35.0
Investment in net assets of and advances to equity affiliates	0.0								0.0								0.0		0.0		0.0
Total assets	$ 4,648.4								$ 2,384.5								$ 4,648.4		$ 2,384.5		$ 1,123.8

[1] Changes in estimates on projects accounted for under the percentage of completion method favorably impacted income by approximately $27 in fiscal year 2017 and $20 in fiscal year 2016, primarily during the fourth quarter. For additional information, see Note 1, Major Accounting Policies (Revenue Recognition).

[2] Includes the impact of an other-than-temporary impairment of an investment in an equity affiliate. For additional information, see Note 8, Summarized Financial Information of Equity Affiliates.