Basis of Presentation and Accounting Policies - Reconciliation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reconciled Basic and Diluted EPS
Net income	$ 261.4	$ 198.6	$ 687.7	$ 189.6
Less: Allocation to participating securities	(0.3)	(0.1)	(0.7)	(0.2)
Net income available to common shareowners	$ 261.1	$ 198.5	$ 687.0	$ 189.4
Basic weighted average outstanding shares (in shares)	117.6	124.4	119.0	126.5
Effect of dilutive securities
Stock options (in shares)	1.0	1.2	0.9	1.4
Performance shares (in shares)	0.0	0.2	0.1	0.2
Diluted weighted average outstanding shares (in shares)	118.6	125.8	120.0	128.1
Earnings per share:
Basic (in usd per share)	$ 2.22	$ 1.60	$ 5.77	$ 1.50
Diluted (in usd per share)	$ 2.20	$ 1.58	$ 5.73	$ 1.48