CONSOLIDATED STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net (loss) income	$ (686.1)	$ 867.9	$ 1,909.3
Other comprehensive (loss) income, net of tax:
Foreign currency translation loss	(215.0)	(143.4)	(234.4)
Derivatives:
Deferred (loss) gain on cash flow hedges	(10.0)	1.1	0.0
Reclassification adjustment of net loss (gain) on cash flow hedges included in earnings	3.6	(0.2)	0.5
Unrealized gain on available for sale security	0.0	0.0	0.8
Reclassification adjustment of gain on available for sale security included in earnings	0.0	0.0	(1.5)
Defined benefit pension and other postretirement benefit plans:
Net actuarial gain (loss) arising during period	24.2	(248.5)	(13.1)
Amortization and settlement recognition of net actuarial loss, included in pension and postretirement cost	35.4	17.2	15.0
Prior service cost arising during period	(19.6)	(3.3)	(5.5)
Amortization and curtailment recognition of prior service cost, included in pension and postretirement cost	3.8	1.8	0.2
Other comprehensive (loss) income, net of tax	(177.6)	(375.3)	(238.0)
Comprehensive (loss) income	(863.7)	492.6	1,671.3
Less: Comprehensive income attributable to noncontrolling interests	(4.5)	(3.6)	(3.2)
Comprehensive (loss) income attributable to common stockholders	$ (868.2)	$ 489.0	$ 1,668.1