Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net sales	$ 1,979.5	$ 1,976.3
Operating Income (Loss)	196.0	270.7
Non-operating pension expense	1.1	(2.0)
Interest expense, net	(9.6)	(15.4)
Income before taxes	187.5	253.3
Trade
Segment Reporting Information [Line Items]
Net sales	1,979.5	1,976.3
Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,979.5	1,976.3
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(44.2)	(43.7)
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(44.2)	(43.7)
Packaging
Segment Reporting Information [Line Items]
Net sales	1,798.3	1,808.6
Operating Income (Loss)	203.8	268.0
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,793.5	1,803.5
Packaging | Intersegment
Segment Reporting Information [Line Items]
Net sales	4.8	5.1
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,798.3	1,808.6
Paper
Segment Reporting Information [Line Items]
Net sales	163.8	150.9
Operating Income (Loss)	29.7	34.1
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	163.8	150.9
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	163.8	150.9
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	17.4	16.8
Operating Income (Loss)	(37.5)	(31.4)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	22.2	21.9
Corporate and Other | Intersegment
Segment Reporting Information [Line Items]
Net sales	39.4	38.6
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 61.6	$ 60.5