Restructuring and Other Costs - Schedule of Restructuring Charges Related to Active Restructuring Initiatives (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	$ 362.9	$ 4.1	$ 365.0	$ 10.7
Restructuring and Related Cost, Cost Incurred to Date	[1]	598.0		598.0
Restructuring and Related Cost, Expected Cost	[1]	689.0		689.0
PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	344.7		345.6	0.2
Restructuring and Related Cost, Cost Incurred to Date	[1]	412.6		412.6
Restructuring and Related Cost, Expected Cost	[1]	412.6		412.6
Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	16.4	1.3	17.8	5.7
Restructuring and Related Cost, Cost Incurred to Date	[1]	142.9		142.9
Restructuring and Related Cost, Expected Cost	[1]	145.0		145.0
Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	1.8	2.8	1.6	4.8
Restructuring and Related Cost, Cost Incurred to Date	[1]	42.5		42.5
Restructuring and Related Cost, Expected Cost	[1]	131.4		131.4
Corporate, Non-Segment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.9	0.7	2.3	2.4
Restructuring and Related Cost, Cost Incurred to Date		69.9		69.9
Restructuring and Related Cost, Expected Cost		69.9		69.9
Corporate, Non-Segment [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.3		1.2
Restructuring and Related Cost, Cost Incurred to Date		10.1		10.1
Restructuring and Related Cost, Expected Cost		10.1		10.1
Corporate, Non-Segment [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost			(0.7)		0.9
Restructuring and Related Cost, Cost Incurred to Date		59.5		59.5
Restructuring and Related Cost, Expected Cost		59.5		59.5
Corporate, Non-Segment [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.6	1.4	1.1	1.5
Restructuring and Related Cost, Cost Incurred to Date		0.3		0.3
Restructuring and Related Cost, Expected Cost		0.3		0.3
Corrugated Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		4.5	0.1	4.4	0.3
Restructuring and Related Cost, Cost Incurred to Date		46.9		46.9
Restructuring and Related Cost, Expected Cost		55.8		55.8
Corrugated Packaging [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date		3.6		3.6
Restructuring and Related Cost, Expected Cost		3.6		3.6
Corrugated Packaging [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		4.4	(0.3)	4.0	(1.0)
Restructuring and Related Cost, Cost Incurred to Date		32.7		32.7
Restructuring and Related Cost, Expected Cost		32.7		32.7
Corrugated Packaging [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.1	0.4	0.4	1.3
Restructuring and Related Cost, Cost Incurred to Date		10.6		10.6
Restructuring and Related Cost, Expected Cost		19.5		19.5
Consumer Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.4	3.2	3.2	7.9
Restructuring and Related Cost, Cost Incurred to Date		47.2		47.2
Restructuring and Related Cost, Expected Cost		47.2		47.2
Consumer Packaging [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost					0.2
Restructuring and Related Cost, Cost Incurred to Date		3.3		3.3
Restructuring and Related Cost, Expected Cost		3.3		3.3
Consumer Packaging [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.3	2.3	3.1	5.8
Restructuring and Related Cost, Cost Incurred to Date		33.3		33.3
Restructuring and Related Cost, Expected Cost		33.3		33.3
Consumer Packaging [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.1	0.9	0.1	1.9
Restructuring and Related Cost, Cost Incurred to Date		10.6		10.6
Restructuring and Related Cost, Expected Cost		10.6		10.6
Paper [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		355.1	0.1	355.1	0.1
Restructuring and Related Cost, Cost Incurred to Date		434.0		434.0
Restructuring and Related Cost, Expected Cost		516.1		516.1
Paper [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		344.4		344.4
Restructuring and Related Cost, Cost Incurred to Date		395.6		395.6
Restructuring and Related Cost, Expected Cost		395.6		395.6
Paper [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		10.7		10.7
Restructuring and Related Cost, Cost Incurred to Date		17.4		17.4
Restructuring and Related Cost, Expected Cost		19.5		19.5
Paper [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost			$ 0.1		$ 0.1
Restructuring and Related Cost, Cost Incurred to Date		21.0		21.0
Restructuring and Related Cost, Expected Cost		$ 101.0		$ 101.0

[1] The Cumulative and Total Expected columns each exclude approximately $2 million for aggregate Land and Development segment and Distribution segment restructuring charges that were incurred in prior periods since the table includes no current year or prior year period activity for those segments.