Business Segment and Geographic Information (Schedule of Operating Income Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Segment Reporting Information [Line Items]
Cost reduction plan	$ 0	[1]	$ 0	[1]	$ (86.8)	[1]	$ 0	[1]
Net loss on Airgas transaction			0				(48.5)
Other operating income	(2.6)	[2]	(3.4)	[2]	(10.4)	[2]	(11.1)	[2]
Operating income	482.8		387.7		1,124.5		1,112.7
Merchant Gases [Member]
Segment Reporting Information [Line Items]
Cost reduction plan					(77.3)
Operating income	164.6		158.7		483.4		500.1
Tonnage Gases [Member]
Segment Reporting Information [Line Items]
Cost reduction plan					(3.8)
Operating income	134.3		114.8		371.1		351.4
Electronics and Performance Materials [Member]
Segment Reporting Information [Line Items]
Cost reduction plan					(5.7)
Operating income	176.7	[3]	109.0	[3]	340.3	[3]	269.5	[3]
Equipment and Energy [Member]
Segment Reporting Information [Line Items]
Operating income	9.8		8.6		26.9		51.3
Segment Total [Member]
Segment Reporting Information [Line Items]
Operating income	$ 485.4		$ 391.1		$ 1,221.7		$ 1,172.3

[1] Information about how this charge related to the businesses at the segment level is discussed in Note 4, Cost Reduction Plan.

[2] Includes stranded costs resulting from discontinued operations.

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