Airgas Transaction (Narratives) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								5 Months Ended	12 Months Ended
	Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Feb. 16, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Airgas Transaction [Abstract]
Number of shares purchased prior to tender offer									1.5
Cost of stock purchased prior to tender offer									$ 69.6	$ 0	$ 0	$ 69.6
Number of shares sold									1.5
Proceeds from sale of Airgas stock									94.7	0	94.7	0
Recognized gain on sale of stock									25.1
Recognized gain on sale of stock, after tax									15.9
Recognized gain on sale of stock, per share									$ 0.07
Net loss on Airgas transaction	0	[1]	0	[1]	5.0	[1]	43.5	[1]		0	48.5	96.0
Net loss on Airgas transaction, after-tax											31.6	60.1
Net loss on Airgas transaction, per share											$ 0.14	$ 0.28
Payment of acquisition-related costs										$ 0	$ 156.2	$ 12.0

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