CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net income	$ 139.5	$ 139.8
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	100.4	(64.9)
Derivatives:
Deferred loss on cash flow hedges	(0.5)
Reclassification adjustment of net gain on cash flow hedges included in earnings	(1.3)
Defined benefit pension and other postretirement benefit plans:
Amortization and settlement recognition of net actuarial loss, included in pension cost	8.7	4.9
Amortization and settlement recognition of prior service cost, included in pension cost	0.5	0.5
Other comprehensive income (loss), net of tax	107.8	(59.5)
Comprehensive income	247.3	80.3
Less: Comprehensive income attributable to noncontrolling interests	(1.1)	(0.7)
Comprehensive income attributable to common stockholders	$ 246.2	$ 79.6