Restructuring and Other Costs - Schedule of Restructuring Charges Related to Active Restructuring Initiatives (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	$ (1.8)	$ 7.0	$ 363.2	$ 17.7
Restructuring and Related Cost, Cost Incurred to Date	[1]	596.2		596.2
Restructuring and Related Cost, Expected Cost	[1]	680.9		680.9
PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	(6.8)		338.8	0.2
Restructuring and Related Cost, Cost Incurred to Date	[1]	405.7		405.7
Restructuring and Related Cost, Expected Cost	[1]	405.7		405.7
Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	0.8	4.5	18.6	10.2
Restructuring and Related Cost, Cost Incurred to Date	[1]	143.8		143.8
Restructuring and Related Cost, Expected Cost	[1]	146.0		146.0
Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost	[1]	4.2	2.5	5.8	7.3
Restructuring and Related Cost, Cost Incurred to Date	[1]	46.7		46.7
Restructuring and Related Cost, Expected Cost	[1]	129.2		129.2
Corrugated Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.1	1.3	5.5	1.6
Restructuring and Related Cost, Cost Incurred to Date		48.0		48.0
Restructuring and Related Cost, Expected Cost		54.6		54.6
Corrugated Packaging [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.3		0.3
Restructuring and Related Cost, Cost Incurred to Date		3.9		3.9
Restructuring and Related Cost, Expected Cost		3.9		3.9
Corrugated Packaging [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.2	0.3	4.2	(0.7)
Restructuring and Related Cost, Cost Incurred to Date		32.9		32.9
Restructuring and Related Cost, Expected Cost		32.9		32.9
Corrugated Packaging [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.6	1.0	1.0	2.3
Restructuring and Related Cost, Cost Incurred to Date		11.2		11.2
Restructuring and Related Cost, Expected Cost		17.8		17.8
Consumer Packaging [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.4	5.3	4.6	13.2
Restructuring and Related Cost, Cost Incurred to Date		48.6		48.6
Restructuring and Related Cost, Expected Cost		48.6		48.6
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		1.4	4.2	4.5	10.0
Restructuring and Related Cost, Cost Incurred to Date		34.7		34.7
Restructuring and Related Cost, Expected Cost		34.7		34.7
Consumer Packaging [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost			1.1	0.1	3.0
Restructuring and Related Cost, Cost Incurred to Date		10.6		10.6
Restructuring and Related Cost, Expected Cost		10.6		10.6
Global Paper [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(7.1)		348.0	0.1
Restructuring and Related Cost, Cost Incurred to Date		426.8		426.8
Restructuring and Related Cost, Expected Cost		504.9		504.9
Global Paper [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(7.5)		336.9
Restructuring and Related Cost, Cost Incurred to Date		388.1		388.1
Restructuring and Related Cost, Expected Cost		388.1		388.1
Global Paper [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		(0.8)		9.9
Restructuring and Related Cost, Cost Incurred to Date		16.5		16.5
Restructuring and Related Cost, Expected Cost		18.7		18.7
Global Paper [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.2		1.2	0.1
Restructuring and Related Cost, Cost Incurred to Date		22.2		22.2
Restructuring and Related Cost, Expected Cost		98.1		98.1
Distribution [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.0		1.0
Restructuring and Related Cost, Cost Incurred to Date		1.2		1.2
Restructuring and Related Cost, Expected Cost		1.2		1.2
Distribution [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date		0.2		0.2
Restructuring and Related Cost, Expected Cost		0.2		0.2
Distribution [Member] | Other Restructuring Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.0		1.0
Restructuring and Related Cost, Cost Incurred to Date		1.0		1.0
Restructuring and Related Cost, Expected Cost		1.0		1.0
Corporate, Non-Segment [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		1.8	0.4	4.1	2.8
Restructuring and Related Cost, Cost Incurred to Date		71.6		71.6
Restructuring and Related Cost, Expected Cost		71.6		71.6
Corporate, Non-Segment [Member] | PP&E and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost		0.4		1.6
Restructuring and Related Cost, Cost Incurred to Date		10.4		10.4
Restructuring and Related Cost, Expected Cost		10.4		10.4
Corporate, Non-Segment [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and Related Cost, Incurred Cost					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		1.4	$ 0.4	2.5	$ 1.9
Restructuring and Related Cost, Cost Incurred to Date		1.7		1.7
Restructuring and Related Cost, Expected Cost		$ 1.7		$ 1.7

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