Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales		$ 1,733.7	$ 1,690.6
Operating Income (Loss)		275.4	212.9	[1]
Non-operating pension expense		(2.0)	(0.5)	[1]
Interest expense, net		(24.1)	(25.8)	[1]
Income before taxes		249.3	186.6	[1]
Trade
Segment Reporting Information [Line Items]
Net sales		1,733.7	1,690.6
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales		(40.3)	(35.3)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales		(40.3)	(35.3)
Packaging
Segment Reporting Information [Line Items]
Net sales		1,477.6	1,402.9
Operating Income (Loss)	[1]	249.6	224.7	[2]
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales		1,470.8	1,396.6
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales		6.8	6.3
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales		1,477.6	1,402.9
Paper
Segment Reporting Information [Line Items]
Net sales		239.7	269.4
Operating Income (Loss)	[1]	45.6	7.2	[2]
Paper | Trade
Segment Reporting Information [Line Items]
Net sales		239.7	269.4
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales		239.7	269.4
Corporate and Other
Segment Reporting Information [Line Items]
Net sales		16.4	18.3
Operating Income (Loss)		(19.8)	(19.0)	[1],[2]
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales		23.2	24.6
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales		33.5	29.0
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales		$ 56.7	$ 53.6

[1] Includes $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.

[2] Includes $8.8 million 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 and $0.3 million of charges consisting of closure costs related to corrugated products facilities and a corporate administration facility.