Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Segment Reporting Information [Line Items]
Net sales	$ 1,541.6		$ 1,759.9	$ 3,250.3		$ 3,493.6
Operating Income (Loss)	116.1		280.4	325.2		555.8
Non-operating pension income and expense	0.6		(2.0)	1.1		(4.1)
Interest expense, net	(25.1)		(22.4)	(44.6)		(46.4)
Income before taxes	91.6		256.0	281.7		505.3
Trade
Segment Reporting Information [Line Items]
Net sales	1,541.6		1,759.9	3,250.3		3,493.6
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(42.1)		(38.3)	(78.5)		(78.6)
Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,541.6		1,759.9	3,250.3		3,493.6
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(42.1)		(38.3)	(78.5)		(78.6)
Packaging
Segment Reporting Information [Line Items]
Net sales	1,409.9		1,504.6	2,877.4		2,982.2
Operating Income (Loss)	197.6	[1]	263.9	397.5	[1]	513.4	[2]
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,401.8		1,497.8	2,867.2		2,968.6
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	8.1		6.8	10.2		13.6
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,409.9		1,504.6	2,877.4		2,982.2
Paper
Segment Reporting Information [Line Items]
Net sales	123.3		237.8	340.7		477.5
Operating Income (Loss)	(61.4)	[1],[3]	38.8	(29.0)	[1],[3]	84.4	[2]
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	123.3		237.8	340.7		477.5
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	123.3		237.8	340.7		477.5
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	8.4		17.5	32.2		33.9
Operating Income (Loss)	(20.1)		(22.3)	(43.3)		(42.0)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	16.5		24.3	42.4		47.5
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	34.0		31.5	68.3		65.0
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 50.5		$ 55.8	$ 110.7		$ 112.5

[1] The three and six months ended June 30, 2020 include the following:

1. $20.4 million and $20.8 million, respectively, consisting of closure costs related to corrugated products facilities, substantially all of which relates to the previously announced closure of the San Lorenzo, California facility during the second quarter, partially offset by income related to the sale of a corrugated products facility.

2. $6.1 million and $6.9 million, respectively, of incremental, out-of-pocket costs related to COVID-19, including supplies, cleaning and sick pay.

[2] The six months ended June 30, 2019 include $0.6 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 produce virgin kraft linerboard.

[3] During the second quarter of 2020, with the exacerbated deterioration in uncoated freesheet market conditions and the estimated impact on our Paper reporting unit arising from the COVID-19 pandemic, as well as projected future results of operations, we identified a triggering event indicating possible impairment of goodwill within our Paper reporting unit. The Company performed an interim quantitative impairment analysis as of May 31, 2020, and, based on the evaluation performed, we determined that goodwill was fully impaired for the Paper reporting unit and recognized a non-cash impairment charge of $55.2 million. See Note 9, Goodwill and Intangible Assets, for additional information.