Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 80.3	$ (236.4)
Other comprehensive (loss) income, net of tax:
Pension and other postretirement benefit plan adjustments (net of tax expense of $4.3 and $7.4)	13.8	20.2
Currency translation adjustments	(28.5)	(16.1)
Net change in unrealized gains and losses on cash flow hedges (net of tax benefit of $6.5 and $0.3)	(20.8)	0.5
Net change in unrealized gains and losses on available-for-sale investments (net of tax benefit of $0.1 and $0.3)	0.5	(1.1)
Other comprehensive (loss) income	(35.0)	3.5
Comprehensive income (loss)	$ 45.3	$ (232.9)