Consolidated Statement of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net unrealized losses on derivative instruments, tax	$ 3.1	$ 0.9	$ 5.3
Reclassification of net unrealized losses on derivatives, tax	1.1	3.6	4.0
Net unrealized gains (losses) in pension and other post retirment benefits, tax	6.0	6.2	4.6
Reclassification net pension and postretirement benefit income (loss), tax	$ 2.3	$ 1.1	$ 1.9