Other Comprehensive Income (Loss) - Schedule of reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Affected Line in the Consolidated Statement of Operations:
Net revenue	$ 722.3	$ 648.9	$ 1,414.8	$ 1,215.8
Cost of goods sold	(476.4)	(455.2)	(924.7)	(850.3)
Other income, net	1.0	2.3	0.6	4.2
Tax expense	(30.4)	(1.8)	(61.7)	10.6
Total reclassifications for the period, net of tax			2.7	3.0
Amortization of Pension and Postretirement
Affected Line in the Consolidated Statement of Operations:
Total reclassifications for the period, net of tax			1.8	2.5
Derivative Instruments
Affected Line in the Consolidated Statement of Operations:
Total reclassifications for the period, net of tax			0.9	0.5
Reclassifications out of accumulated other comprehensive income (loss)
Affected Line in the Consolidated Statement of Operations:
Net revenue	0.2	(0.3)	0.2	(0.2)
Cost of goods sold	(0.3)	(0.2)	(0.3)	(0.4)
Other income, net	1.6	2.3	3.4	4.4
Total before tax	1.5	1.8	3.3	3.8
Tax expense	(0.4)	(0.3)	(0.6)	(0.8)
Total reclassifications for the period, net of tax	1.1	1.5	2.7	3.0
Reclassifications out of accumulated other comprehensive income (loss) | Net Loss Recognized
Affected Line in the Consolidated Statement of Operations:
Net revenue	0.0	0.0	0.0	0.0
Cost of goods sold	0.0	0.0	0.0	0.0
Other income, net	1.2	1.9	2.5	3.5
Total before tax	1.2	1.9	2.5	3.5
Reclassifications out of accumulated other comprehensive income (loss) | Prior Service Costs Recognized
Affected Line in the Consolidated Statement of Operations:
Net revenue	0.0	0.0	0.0	0.0
Cost of goods sold	0.0	0.0	0.0	0.0
Other income, net	(0.1)	(0.1)	(0.1)	(0.1)
Total before tax	(0.1)	(0.1)	(0.1)	(0.1)
Reclassifications out of accumulated other comprehensive income (loss) | Derivative Instruments
Affected Line in the Consolidated Statement of Operations:
Net revenue	0.2	(0.3)	0.2	(0.2)
Cost of goods sold	(0.3)	(0.2)	(0.3)	(0.4)
Other income, net	0.5	0.5	1.0	1.0
Total before tax	$ 0.4	$ 0.0	$ 0.9	$ 0.4