Earnings per share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net earnings for basic and dilutive earnings per share	$ 129.8	$ 143.8
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted-average shares for basic earnings per share	61.8	66.2
Effect of dilutive securities:
Stock options	0.1	0.2
Restricted stock equivalents	0.7	0.5
Total dilutive securities	0.8	0.7
Weighted-average shares for diluted earnings per share	62.6	66.9
Basic net earnings per share	$ 2.10	$ 2.17
Diluted net earnings per share	$ 2.07	$ 2.15
Antidilutive securities excluded from computation of EPS	0.4	0.6