Business Segment and Geographic Information (Schedule of Income Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended			12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012		Mar. 31, 2013	Mar. 31, 2012		Sep. 30, 2012
Segment Reporting Information [Line Items]
Business restructuring and cost reduction plans	$ 0	$ 86.8	[1]	$ 0	$ 86.8	[1]	$ 327.4
Other operating income	0.3	1.5		(6.1)	(7.8)
Operating income	389.7	287.9		762.1	641.7
Merchant Gases [Member]
Segment Reporting Information [Line Items]
Operating income	168.1	152.5		339.1	318.8
Tonnage Gases [Member]
Segment Reporting Information [Line Items]
Operating income	123.2	125.4		261.3	236.8
Electronics and Performance Materials [Member]
Segment Reporting Information [Line Items]
Operating income	77.5	85.5		138.8	163.6
Equipment and Energy [Member]
Segment Reporting Information [Line Items]
Operating income	20.6	9.8		29.0	17.1
Segment Total [Member]
Segment Reporting Information [Line Items]
Operating income	$ 389.4	$ 373.2		$ 768.2	$ 736.3

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