General Information - Business Combinations and Shutdown and Other Special Charges, Net (Details) $ in Millions				3 Months Ended			9 Months Ended		12 Months Ended
	Apr. 01, 2020 facility	Jan. 31, 2020 USD ($)	Aug. 01, 2019 mill facility	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) mill	Sep. 30, 2019 USD ($)	Dec. 31, 2022 USD ($) mill	Dec. 31, 2019
Business Acquisition [Line Items]
Charges Associated with Business Combinations				$ 0.9		$ 0.6	$ (3.1)	$ 3.2
Shutdown and Other Special Charges				3.7		4.6	29.9	18.1
Exit Activities				4.4		3.0	21.4	3.0
Total				9.0		$ 8.2	$ 48.2	$ 24.3
Number of converting facilities | facility	7
Increase in multi-employer plan withdrawal obligation				12.2	$ 12.2
Number of mills to be closed | mill							2
Number of facilities acquired | facility			2
Length of program to dismantle and dispose of abandoned assets										3 years
Artistic Carton Company
Business Acquisition [Line Items]
Number of mills acquired | mill			1
Quad/Graphics, Inc.
Business Acquisition [Line Items]
Bargain purchase gain		$ 6.6			$ 6.6
Paperboard Mills
Business Acquisition [Line Items]
Expected costs associated with closures				$ 40.0			$ 40.0
Forecast | Facility Closing
Business Acquisition [Line Items]
Number of mills to be closed | mill									2
Forecast | Construction in Progress
Business Acquisition [Line Items]
Investment in new CRB Mill									$ 600.0