Basis of Presentation and Accounting Policies (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Reconciled Basic and Diluted EPS
Net income	$ 189.5	$ 168.0	$ 404.2	$ 353.5
Less: Allocation to participating securities	(0.2)	(0.2)	(0.4)	(0.4)
Net income available to common shareowners	$ 189.3	$ 167.8	$ 403.8	$ 353.1
Basic weighted average outstanding shares	128.7	130.5	128.5	131.2
Effect of dilutive securities
Stock options	1.3	0.8	1.3	0.8
Performance shares	0.3	0.0	0.2	0.0
Diluted weighted average outstanding shares	130.3	131.3	130.0	132.0
Basic earnings per share:
Basic	$ 1.47	$ 1.29	$ 3.14	$ 2.69
Diluted earnings per share:
Diluted	$ 1.45	$ 1.28	$ 3.11	$ 2.68