Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Tax on (loss) gain on derivative instruments	$ (3.4)	$ 2.4	$ 10.9	$ (11.9)
Tax on reclassification on derivative instruments	(0.4)	(1.9)	5.5	(2.3)
Tax on foreign currency adjustments	0.0	(55.3)	0.0	(4.7)
Tax on benefit plans	$ (0.3)	$ (0.1)	$ (0.7)	$ (0.7)