Condensed Consolidated Statement of Comprehensive (Loss) Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss), Tax, Parenthetical Disclosures [Abstract]
Pension and other postretirement benefit plan adjustments (net of tax expense of $7.4 and $12.8)	$ 7.4	$ 12.8
Net change in unrealized gains and losses on cash flow hedges (net of tax (benefit) expense of ($0.3) and $4.0)	(0.3)	4.0
Net change in unrealized gains and losses on available-for-sale investments (net of tax benefit of $0.3 and $0.0)	$ 0.3	$ 0.0