Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Tax on (loss) gain on derivative instruments	$ (12.2)	$ (7.2)	$ 29.3
Tax on reclassifications on derivative instruments	2.0	(10.3)	(14.6)
Tax on foreign currency translation	13.8	(6.6)	2.8
Tax on foreign currency gain and losses on long-term intra-company transactions	10.6	(0.8)	0.7
Tax on benefit plans	2.6	(3.8)	6.0
Tax on reclassification of benefit plans and prior service costs	$ (0.6)	$ (0.8)	$ (0.5)