Condensed Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Tax on (loss) gain on derivative instruments	$ 0.4	$ (4.4)	$ (7.1)	$ (3.0)
Tax on reclassifications on derivative instruments	3.3	(4.2)	5.3	(7.7)
Tax on foreign currency adjustments	0.6	8.2	(3.1)	4.2
Tax on benefit plans	$ (0.1)	$ (0.3)	$ 0	$ (0.5)