Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Net sales	$ 1,976.3	$ 2,136.4
Operating Income (Loss)	270.7	356.5
Non-operating pension expense	(2.0)	3.6
Interest expense, net	(15.4)	(19.8)
Income before taxes	253.3	340.3
Trade
Segment Reporting Information [Line Items]
Net sales	1,976.3	2,136.4
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(43.7)	(39.9)
Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,976.3	2,136.4
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(43.7)	(39.9)
Segment Reconciling Items | Trade
Segment Reporting Information [Line Items]
Net sales	0.0
Packaging
Segment Reporting Information [Line Items]
Net sales	1,808.6	1,964.5
Operating Income (Loss)	268.0	362.2
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,803.5	1,960.0
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	5.1	4.5
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,808.6	1,964.5
Paper
Segment Reporting Information [Line Items]
Net sales	150.9	153.5
Operating Income (Loss)	34.1	22.4
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	150.9	153.5
Paper | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	0.0
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	150.9	153.5
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	16.8	18.4
Operating Income (Loss)	(31.4)	(28.1)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	21.9	22.9
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	38.6	35.4
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 60.5	$ 58.3