Earnings Per Share (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Number of shares excluded from computation of earnings per share	6.7	4.0
Earnings Per Share Reconciliation [Abstract]
Net income	$ 123.2	$ 66.3
Interest expense and amortization of issuance costs associated with convertible senior notes	6.8	5.7
Numerator for diluted earnings per share after assumed conversions	$ 130.0	$ 72.0
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Denominator for basic earnings per share - weighted average common shares	323.1	321.1
Employee stock awards	2.7	4.4
Incremental Common Shares Attributable to Conversion of Debt Securities	38.6	38.6
Denominator for diluted earnings per share - adjusted weighted average common shares	364.4	364.1