Other Expense, Net - Components of Other Income (Expense), Net (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset disposals and write-offs		$ (6.4)	$ (5.5)	$ (27.3)	$ (16.5)
Facilities closure and other income (costs)	[1]	(0.7)	(2.9)	2.7	(16.6)
Other		(3.1)	(0.4)	(11.0)	(3.8)
Total		(13.4)	(8.8)	(41.7)	(36.9)
Jackson, Alabama Mill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Conversion-related activities	[2]	$ (3.2)	$ 0.0	$ (6.1)	$ 0.0

[1] For the three months ended September 30, 2021, includes charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities, partially offset by closure costs related to corrugated products facilities. For 2020, includes costs primarily related to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020.

[2] Includes charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities.