Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2019		Jun. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 1,759.9	$ 1,767.5		$ 3,493.6		$ 3,458.1
Operating Income (Loss)	280.4	269.6		555.8		482.5
Non-operating pension expense	(2.0)	(0.5)		4.1		1.1
Interest expense, net	(22.4)	(23.8)		(46.4)		(49.6)
Income before taxes	256.0	245.3		505.3		431.8
Trade
Segment Reporting Information [Line Items]
Net sales	1,759.9	1,767.5		3,493.6		3,458.1
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(38.3)	(40.1)		(78.6)		(75.4)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(38.3)	(40.1)		(78.6)		(75.4)
Packaging
Segment Reporting Information [Line Items]
Net sales	1,504.6	1,496.2		2,982.2		2,899.1
Operating Income (Loss)	263.9	273.2	[1]	513.4	[2]	497.9	[1]
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,497.8	1,489.6		2,968.6		2,886.3
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	6.8	6.6		13.6		12.8
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,504.6	1,496.2		2,982.2		2,899.1
Paper
Segment Reporting Information [Line Items]
Net sales	237.8	250.8		477.5		520.2
Operating Income (Loss)	38.8	16.2	[1]	84.4	[2]	23.5	[1]
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	237.8	250.8		477.5		520.2
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	237.8	250.8		477.5		520.2
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	17.5	20.5		33.9		38.8
Operating Income (Loss)	(22.3)	(19.8)	[1]	(42.0)		(38.9)	[1]
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	24.3	27.1		47.5		51.6
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	31.5	33.5		65.0		62.6
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 55.8	$ 60.6		$ 112.5		$ 114.2

[1] (b) Includes the following:   1. For the three and six months ended June 30, 2018, $13.6 million and $22.4 million, respectively, of charges related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side grades at the Wallula, Washington mill associated with the conversion of the No. 3 paper machine to a high-performance 100% virgin kraft linerboard machine.     2. For the three and six months ended June 30, 2018, $0.2 million and $0.5 million, respectively, of charges consisting of closure costs related to corrugated products facilities and a corporate administration facility.

[2] The six months ended June 30, 2019 include $0.6 million of charges related to the announced second quarter 2018 discontinuation of uncoated free sheet and coated one-side grades at the Wallula, Washington mill associated with the conversion of the No. 3 paper machine to a high-performance 100% virgin kraft linerboard machine.