Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Tax on (loss) gain on derivative instruments	$ (8.0)	$ (12.2)	$ (7.2)
Tax on reclassifications on derivative instruments	(2.8)	2.0	(10.3)
Tax on foreign currency translation	(1.0)	13.8	(6.6)
Tax on foreign currency gain and losses on long-term intra-company transactions	(6.7)	10.6	(0.8)
Tax on benefit plans	1.4	2.6	(3.8)
Tax on reclassification of benefit plans and prior service costs	$ (0.8)	$ (0.6)	$ (0.8)