Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Net sales	$ 1,952.1	$ 2,237.3	$ 3,928.4	$ 4,373.7
Operating Income (Loss)	284.4	415.8	555.0	772.4
Non-operating pension expense	(2.0)	3.6	(4.0)	7.3
Interest expense, net	(14.6)	(18.8)	(29.9)	(38.7)
Income before taxes	267.8	400.6	521.1	741.0
Trade
Segment Reporting Information [Line Items]
Net sales	1,952.1	2,237.3	3,928.4	4,373.7
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(42.0)	(42.6)	(85.8)	(82.4)
Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,952.1	2,237.3	3,928.4	4,373.7
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(42.0)	(42.6)	(85.8)	(82.4)
Segment Reconciling Items | Trade
Segment Reporting Information [Line Items]
Net sales	0.0	0.0	0.0	0.0
Packaging
Segment Reporting Information [Line Items]
Net sales	1,790.3	2,066.9	3,598.9	4,031.3
Operating Income (Loss)	285.8	419.8	553.7	782.1
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,785.7	2,061.7	3,589.1	4,021.6
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	4.6	5.2	9.8	9.7
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,790.3	2,066.9	3,598.9	4,031.3
Paper
Segment Reporting Information [Line Items]
Net sales	142.8	149.8	293.7	303.3
Operating Income (Loss)	29.1	22.7	63.2	45.1
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	142.8	149.8	293.7	303.3
Paper | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	0.0	0.0	0.0	0.0
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	142.8	149.8	293.7	303.3
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	19.0	20.6	35.8	39.1
Operating Income (Loss)	(30.5)	(26.7)	(61.9)	(54.8)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	23.6	25.8	45.6	48.8
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	37.4	37.4	76.0	72.7
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 61.0	$ 63.2	$ 121.6	$ 121.5