Goodwill and Intangible Assets -Goodwill - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended	9 Months Ended
	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill [Line Items]
Goodwill impairment charge		$ 0.0	$ 0.0			$ 0.0	$ 55.2
Discount rate utilized	0.09
Alternative Investment, Valuation Technique [Extensible List]	us-gaap:IncomeApproachValuationTechniqueMember
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember
Goodwill		863.5				863.5		$ 863.5
Packaging
Goodwill [Line Items]
Goodwill		$ 863.5				$ 863.5		$ 863.5
Paper
Goodwill [Line Items]
Recoverability test results recoverable percentage	100.00%
Paper Reporting Unit
Goodwill [Line Items]
Goodwill impairment charge	$ 55.2			$ 55.2	$ 55.2