Other Expense, Net - Components of Other Expense, Net (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset disposals and write-offs	[1]	$ (26.5)	$ (25.0)	$ (17.3)
Facilities closure and other costs	[2]	(19.1)	(0.3)	(1.6)
Insurance deductible for property damage	[3]			(0.5)
Acquisition and integration related costs	[4]			(0.2)
Other		(5.1)	(6.7)	(6.7)
Total		$ (50.7)	(32.7)	(41.2)
Wallula, Washington Mill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring	[5]		$ (0.7)	$ (14.9)

[1] For 2019, includes $3.0 million of charges for the disposal of fixed assets related to the containerboard mill conversion at our DeRidder, Louisiana mill.

[2] For 2020, includes charges consisting of restructuring costs for paper administrative functions and closure costs related to corrugated products facilities, substantially all of which relates to the previously announced closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a closed corrugated products facility during the second quarter of 2020. For 2019, includes charges consisting of closure costs related to corrugated products facilities, partially offset by income from the sale of a building related to a closed corrugated products facility. For 2018, includes charges consisting of closure costs related to corrugated products facilities.

[3] Includes charges for the property damage insurance deductible for a weather-related incident at one of our corrugated products facilities.

[4] Includes charges for acquisition and integration costs related to recent acquisitions.

[5] Includes charges related to the discontinuation of production of uncoated free sheet and coated one-side white paper grades at the Wallula, Washington mill in the second quarter of 2018 and the conversion of the No. 3 paper machine to produce virgin kraft linerboard.