Basis of Presentation and Accounting Policies (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Reconciled Basic and Diluted EPS
Net income	$ 204.6	$ 216.9	$ 189.5	$ 214.7	$ 185.2	$ 191.0	$ 168.0	$ 185.5	$ 825.7	$ 729.7	$ 827.6
Less: Allocation to participating securities									(0.9)	(0.7)	(0.7)
Net income available to common shareowners									$ 824.8	$ 729.0	$ 826.9
Basic weighted average outstanding shares									128.4	130.2	134.5
Effect of dilutive securities
Stock options									1.2	0.9	1.1
Performance shares									0.3	0.0	0.1
Diluted weighted average outstanding shares									129.9	131.1	135.7
Basic earnings per share:
Basic	$ 1.59	$ 1.69	$ 1.47	$ 1.67	$ 1.44	$ 1.47	$ 1.29	$ 1.41	$ 6.42	$ 5.60	$ 6.15
Diluted earnings per share:
Diluted	$ 1.57	$ 1.67	$ 1.45	$ 1.65	$ 1.43	$ 1.46	$ 1.28	$ 1.40	$ 6.35	$ 5.56	$ 6.09