CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net income	$ 161.9	$ 224.5	$ 301.7	$ 1,358.0
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	25.2	54.2	(39.7)	12.3
Derivatives:
Deferred gain on cash flow hedges		0.1
Reclassification adjustment of net loss on cash flow hedges included in earnings				0.5
Unrealized gain on available for sale security				0.8
Reclassification adjustment of gain on available for sale security included in earnings		(1.5)		(1.5)
Defined benefit pension and other postretirement benefit plans:
Amortization and settlement recognition of net actuarial loss, included in pension cost	3.2	3.3	8.1	6.6
Prior service cost arising during the period				(2.7)
Amortization and settlement recognition of prior service cost, included in pension cost	0.4		0.9
Other comprehensive income (loss), net of tax	28.8	56.1	(30.7)	16.0
Comprehensive income	190.7	280.6	271.0	1,374.0
Less: Comprehensive income attributable to noncontrolling interests	(1.0)	(1.5)	(1.7)	(0.1)
Comprehensive income attributable to common stockholders	$ 189.7	$ 279.1	$ 269.3	$ 1,373.9