Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Number of shares excluded from computation of earnings per share	2.8
Earnings Per Share Reconciliation [Abstract]
Net income	$ 206.9	$ 157.7
Denominator:
Denominator for basic earnings per share — weighted average common shares	373.3	369.3
Effect of dilutive securities:
Employee stock awards (shares)	4.1	4.2
Denominator for diluted earnings per share — adjusted weighted average common shares	377.4	373.5
Basic net income per common share (in dollars per share)	$ 0.55	$ 0.43
Net income per common share assuming dilution (in dollars per share)	$ 0.55	$ 0.42