Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Net sales	$ 2,136.4	$ 1,807.2
Operating Income (Loss)	356.5	238.3
Non-operating pension income	3.6	4.8
Interest expense, net	(19.8)	(23.5)
Income before taxes	340.3	219.6
Trade
Segment Reporting Information [Line Items]
Net sales	2,136.4	1,807.2
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(39.9)	(36.4)
Operating Segments
Segment Reporting Information [Line Items]
Net sales	2,136.4	1,807.2
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(39.9)	(36.4)
Packaging
Segment Reporting Information [Line Items]
Net sales	1,964.5	1,623.6
Operating Income (Loss)	362.2	257.9
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,960.0	1,619.8
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	4.5	3.8
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,964.5	1,623.6
Paper
Segment Reporting Information [Line Items]
Net sales	153.5	164.6
Operating Income (Loss)	22.4	8.7
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	153.5	164.4
Paper | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales		0.2
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	153.5	164.6
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	18.4	19.0
Operating Income (Loss)	(28.1)	(28.3)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	22.9	23.0
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	35.4	32.4
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 58.3	$ 55.4