Business Segment and Geographic Information (Schedule of Income Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended																12 Months Ended
	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010
Segment Reporting Information [Line Items]
Business restructuring and cost reduction plans	$ (240.6)	[1]	$ 0	[1]	$ (86.8)	[1]	$ 0	[1]									$ (327.4)	[2]	$ 0	[2]	$ 0	[2]
Net loss on Airgas transaction									0	[3]	0	[3]	(5.0)	[3]	(43.5)	[3]	0		(48.5)		(96.0)
Customer bankruptcy	(9.8)	[4]	0	[4]	0	[4]	0	[4]									(9.8)		0		6.4
Pension settlement																	0		0		11.5
Other operating income																	(6.6)	[5]	(39.3)	[5]	(26.7)	[5]
Operating income	157.9		482.8		287.9		353.8		395.4		387.7		393.8		331.2		1,282.4		1,508.1		1,267.7
Depreciation and amortization																	840.8		834.3		826.8
Income (Loss) from Equity Method Investments																	153.8		154.3		126.9
Merchant Gases [Member]
Segment Reporting Information [Line Items]
Operating income																	644.0		668.9		632.2
Depreciation and amortization																	363.2		356.9		341.3
Income (Loss) from Equity Method Investments																	137.1		134.6		104.3
Tonnage Gases [Member]
Segment Reporting Information [Line Items]
Operating income																	512.0		503.1		444.2
Depreciation and amortization																	320.4		310.9		303.0
Electronics and Performance Materials [Member]
Segment Reporting Information [Line Items]
Operating income																	425.6	[6]	361.1	[6]	251.8	[6]
Depreciation and amortization																	144.1		154.9		169.0
Equipment and Energy [Member]
Segment Reporting Information [Line Items]
Operating income																	44.6		62.8		67.3
Depreciation and amortization																	12.2		11.0		12.7
Segment Total [Member]
Segment Reporting Information [Line Items]
Operating income																	1,626.2		1,595.9		1,395.5
Depreciation and amortization																	839.9		833.7		826.0
All Other Segments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization																	0.9		0.6		0.8
Income (Loss) from Equity Method Investments																	$ 16.7		$ 19.7		$ 22.6

[1]   For additional information, see Note 4, Business Restructuring and Cost Reduction Plans.

[2] Information about how this charge related to the businesses at the segment level is discussed in Note 4, Business Restructuring and Cost Reduction Plans.

[3]   For additional information, see Note 6, Airgas Transaction.

[4]   For additional information, see Note 22, Supplemental Information.

[5] Includes stranded costs resulting from discontinued operations.

[6] Includes the gain on remeasuring our previously held equity interest in DA NanoMaterials. For additional information, see Note 5, Business Combinations.