Earnings Per Share (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
Earnings Per Share [Abstract]
Number of shares excluded from computation of earnings per share				6.4
Earnings Per Share Reconciliation [Abstract]
Net income	$ 229.2	$ 195.1	$ 436.1	$ 352.8
Denominator:
Denominator for basic earnings per share — weighted average common shares	374.4	370.2	373.8	369.7
Effect of dilutive securities:
Employee stock awards (shares)	4.5	3.5	4.3	3.9
Denominator for diluted earnings per share — adjusted weighted average common shares	378.9	373.7	378.1	373.6
Basic net income per common share (in dollars per share)	$ 0.61	$ 0.53	$ 1.17	$ 0.95
Net income per common share assuming dilution (in dollars per share)	$ 0.60	$ 0.52	$ 1.15	$ 0.94