Revenue - Summary of Revenues Disaggregated by Product Line (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,541.6	$ 1,759.9	$ 3,250.3	$ 3,493.6
Packaging
Disaggregation Of Revenue [Line Items]
Revenue	1,409.9	1,504.6	2,877.4	2,982.2
Paper
Disaggregation Of Revenue [Line Items]
Revenue	123.3	237.8	340.7	477.5
Corporate and Other
Disaggregation Of Revenue [Line Items]
Revenue	$ 8.4	$ 17.5	$ 32.2	$ 33.9