Earnings Per Share (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Number of shares excluded from computation of earnings per share			9.1	5.6
Earnings Per Share Reconciliation [Abstract]
Net income	$ 131.0	$ 111.0	$ 254.1	$ 177.3
Interest expense and amortization of issuance costs associated with convertible senior notes	6.9	5.8	13.7	11.5
Numerator for diluted earnings per share after assumed conversions	$ 137.9	$ 116.8	$ 267.8	$ 188.8
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Denominator for basic earnings per share - weighted average common shares	324.3	321.7	323.7	321.4
Employee stock awards	3.4	5.1	3.1	4.7
Incremental Common Shares Attributable to Conversion of Debt Securities	38.6	38.6	38.6	38.6
Denominator for diluted earnings per share - adjusted weighted average common shares	366.3	365.4	365.4	364.7