Goodwill (Schedule of Goodwill by Segment) (Details) (USD $)
In Millions, unless otherwise specified
 6 Months Ended 12 Months Ended
Mar. 31, 2015
Sep. 30, 2014
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance $ 1,237.3  
Goodwill, Acquisitions and Adjustments 5.4  
Goodwill, Currency Translation and Other (87.3)  
Goodwill, net, Ending Balance 1,155.4  
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, gross 1,427.6 1,522.1
Goodwill, Accumulated impairment losses (272.2) [1] (284.8) [1]
Goodwill, net 1,155.4  
Industrial Gases - Americas [Member]    
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance 327.2  
Goodwill, Acquisitions and Adjustments 2.2  
Goodwill, Currency Translation and Other (9.8)  
Goodwill, net, Ending Balance 319.6 327.2
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, net 319.6 327.2
Goodwill, Accumulated impairment losses currency translation 33.0 20.4
Industrial Gases - EMEA [Member]    
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance 433.3  
Goodwill, Acquisitions and Adjustments 3.2  
Goodwill, Currency Translation and Other (58.5)  
Goodwill, net, Ending Balance 378.0  
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, net 378.0  
Industrial Gases - Asia [Member]    
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance 140.0  
Goodwill, Acquisitions and Adjustments 0  
Goodwill, Currency Translation and Other (4.0)  
Goodwill, net, Ending Balance 136.0  
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, net 136.0  
Industrial Gases - Global [Member]    
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance 21.4  
Goodwill, Acquisitions and Adjustments 0  
Goodwill, Currency Translation and Other (1.2)  
Goodwill, net, Ending Balance 20.2  
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, net 20.2  
Materials Technologies [Member]    
Goodwill [Roll Forward]    
Goodwill, net, Beginning Balance 315.4  
Goodwill, Acquisitions and Adjustments 0  
Goodwill, Currency Translation and Other (13.8)  
Goodwill, net, Ending Balance 301.6  
Goodwill Impaired Accumulated Impairment Loss Abstract    
Goodwill, net $ 301.6  
[1]
Amount is attributable to the Industrial Gases – Americas segment and includes currency translation of $33.0 and $20.4 as of 31 March 2015 and 30 September 2014, respectively.