Stock-Based Compensation - Narrative (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation [Abstract]
Number of shares authorized for issuance under the USIP	120.0
Number of shares available for grant under USIP	29.6
Stock-based compensation	$ 127.7	$ 113.4	$ 101.3
Unrecognized compensation cost related to nonvested awards net of estimated forfeitures	129.3
Weighted-average remaining contractual term (in years)	1 year 7 months 18 days
Weighted-average grant-date fair values of stock awards and stock unit awards granted	$ 53.89	$ 44.01	$ 35.59
Fair value of stock awards and stock unit awards vested	153.0	126.3	91.7
Total intrinsic values of share options exercised	17.9	43.3	61.2
Cash received from stock option exercises	7.2	18.1	27.7
Income tax benefits from stock options exercises	$ 5.9	$ 19.3	$ 16.7
Total shares issued under ESIP	0.6
Shares reserved for future issuance under ESIP	5.8