Restructuring and Other Costs - Schedule of Restructuring Charges Related to Active Restructuring Initiatives (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	$ 24.7	$ 25.7
Restructuring and Related Cost, Cost Incurred to Date	333.8
Restructuring and Related Cost, Expected Cost	338.4
Net Property, Plant and Equipment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	2.7	3.1
Restructuring and Related Cost, Cost Incurred to Date	128.1
Restructuring and Related Cost, Expected Cost	128.1
Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	20.5	20.6
Restructuring and Related Cost, Cost Incurred to Date	145.5
Restructuring and Related Cost, Expected Cost	145.5
Equipment and Inventory Relocation Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.5	0.7
Restructuring and Related Cost, Cost Incurred to Date	14.6
Restructuring and Related Cost, Expected Cost	16.8
Facility Carrying Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.6	0.9
Restructuring and Related Cost, Cost Incurred to Date	20.9
Restructuring and Related Cost, Expected Cost	22.9
Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.4	0.4
Restructuring and Related Cost, Cost Incurred to Date	24.7
Restructuring and Related Cost, Expected Cost	25.1
Corporate, Non-Segment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	7.7	14.1
Restructuring and Related Cost, Cost Incurred to Date	53.4
Restructuring and Related Cost, Expected Cost	53.4
Corporate, Non-Segment [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	7.7	14.2
Restructuring and Related Cost, Cost Incurred to Date	46.0
Restructuring and Related Cost, Expected Cost	46.0
Corporate, Non-Segment [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(0.1)
Restructuring and Related Cost, Cost Incurred to Date	7.4
Restructuring and Related Cost, Expected Cost	7.4
Corrugated Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	10.5	11.2
Restructuring and Related Cost, Cost Incurred to Date	170.8
Restructuring and Related Cost, Expected Cost	174.6
Corrugated Packaging [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	2.2	3.1
Restructuring and Related Cost, Cost Incurred to Date	96.2
Restructuring and Related Cost, Expected Cost	96.2
Corrugated Packaging [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	7.1	6.6
Restructuring and Related Cost, Cost Incurred to Date	41.6
Restructuring and Related Cost, Expected Cost	41.6
Corrugated Packaging [Member] | Equipment and Inventory Relocation Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.4	0.4
Restructuring and Related Cost, Cost Incurred to Date	8.6
Restructuring and Related Cost, Expected Cost	10.4
Corrugated Packaging [Member] | Facility Carrying Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.6	1.1
Restructuring and Related Cost, Cost Incurred to Date	19.0
Restructuring and Related Cost, Expected Cost	20.7
Corrugated Packaging [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.2
Restructuring and Related Cost, Cost Incurred to Date	5.4
Restructuring and Related Cost, Expected Cost	5.7
Consumer Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	6.5	0.5
Restructuring and Related Cost, Cost Incurred to Date	91.0
Restructuring and Related Cost, Expected Cost	91.8
Consumer Packaging [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.5
Restructuring and Related Cost, Cost Incurred to Date	30.1
Restructuring and Related Cost, Expected Cost	30.1
Consumer Packaging [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	5.7	(0.1)
Restructuring and Related Cost, Cost Incurred to Date	44.1
Restructuring and Related Cost, Expected Cost	44.1
Consumer Packaging [Member] | Equipment and Inventory Relocation Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.1	0.3
Restructuring and Related Cost, Cost Incurred to Date	6.0
Restructuring and Related Cost, Expected Cost	6.4
Consumer Packaging [Member] | Facility Carrying Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(0.2)
Restructuring and Related Cost, Cost Incurred to Date	1.9
Restructuring and Related Cost, Expected Cost	2.2
Consumer Packaging [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	0.2	0.5
Restructuring and Related Cost, Cost Incurred to Date	8.9
Restructuring and Related Cost, Expected Cost	9.0
Land and Development [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(0.1)
Restructuring and Related Cost, Cost Incurred to Date	18.6
Restructuring and Related Cost, Expected Cost	18.6
Land and Development [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	1.8
Restructuring and Related Cost, Expected Cost	1.8
Land and Development [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		$ (0.1)
Restructuring and Related Cost, Cost Incurred to Date	13.8
Restructuring and Related Cost, Expected Cost	13.8
Land and Development [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	3.0
Restructuring and Related Cost, Expected Cost	$ 3.0