Goodwill and Intangible Assets (Schedule of Goodwill by Segment) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Sep. 30, 2012	Sep. 30, 2011
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 796.2	$ 816.9
Goodwill, Acquisitions and Adjustments	765.4	4.9
Goodwill, Currency Translation and Other	36.8	(25.6)
Goodwill, Ending Balance	1,598.4	796.2
Merchant Gases [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	479.2	498.0
Goodwill, Acquisitions and Adjustments	630.0	4.9
Goodwill, Currency Translation and Other	29.4	(23.7)
Goodwill, Ending Balance	1,138.6	479.2
Tonnage Gases [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	14.1	15.5
Goodwill, Acquisitions and Adjustments	0	0
Goodwill, Currency Translation and Other	0.6	(1.4)
Goodwill, Ending Balance	14.7	14.1
Electronics and Performance Materials [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	302.9	303.4
Goodwill, Acquisitions and Adjustments	135.4	0
Goodwill, Currency Translation and Other	6.8	(0.5)
Goodwill, Ending Balance	$ 445.1	$ 302.9

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 34

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 43

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 72

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Change in the carrying value of goodwill. The change could be the result of new goodwill acquired, goodwill impairment, if any, goodwill written off related to the sale of a business or other adjustments to goodwill.

+ References+ Details