Segment Information - Segment Sales to External Customers by Product Line (Details) - USD ($) $ in Millions	3 Months Ended															12 Months Ended
	Dec. 31, 2019	[1]	Sep. 30, 2019	[2]	Jun. 30, 2019	Mar. 31, 2019	[3]	Dec. 31, 2018	[4]	Sep. 30, 2018	[5]	Jun. 30, 2018	[6]	Mar. 31, 2018	[7]	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Segment sales to external customers	$ 1,720.0		$ 1,750.7		$ 1,759.9	$ 1,733.7		$ 1,746.6		$ 1,809.9		$ 1,767.5		$ 1,690.6		$ 6,964.3	$ 7,014.6	$ 6,444.9	[8]
Packaging
Revenue from External Customer [Line Items]
Segment sales to external customers																5,932.2	5,938.5	5,312.3	[8]
Paper
Revenue from External Customer [Line Items]
Segment sales to external customers																964.3	1,002.0	1,051.8	[8]
Operating Segments
Revenue from External Customer [Line Items]
Segment sales to external customers																6,964.3	7,014.6	6,444.9
Operating Segments | Packaging
Revenue from External Customer [Line Items]
Segment sales to external customers																5,932.2	5,938.5	5,312.3
Operating Segments | Paper
Revenue from External Customer [Line Items]
Segment sales to external customers																964.3	1,002.0	1,051.8
Operating Segments | Corporate and Other
Revenue from External Customer [Line Items]
Segment sales to external customers																$ 67.8	$ 74.1	$ 80.8

[1] Includes $0.4 million of charges consisting of closure costs related related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($0.3 million after-tax or $0.00 per diluted share) and $38.7 million of charges related to the Company’s November 2019 debt refinancing, which included redemption premiums and the write-offs of remaining balances of treasury locks and unamortized debt issuance costs as well as $3.2 million of income tax benefit from the stranded tax effects in Accumulated Other Comprehensive Income related to the write-offs of the treasury locks ($25.9 million after-tax or $0.28 per diluted share). Also includes $0.3 million of charges consisting of closure costs related to corrugated products facilities, partially offset by income from the sale of a building related to a closed corrugated products facility ($0.2 million after-tax or $0.00 per diluted share).

[2] Includes $3.0 million of charges for the disposal of fixed assets related to the containerboard mill conversion at our DeRidder, Louisiana mill ($2.3 million after-tax or $0.02 per diluted share).

[3] Includes $0.6 million of charges consisting of closure costs related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($0.5 million after-tax or $0.01 per diluted share).

[4] Includes $3.6 million of charges related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula, Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($2.7 million after-tax or $0.03 per diluted share) and $0.1 million of charges for acquisition and integration costs related to recent acquisitions ($0.1 million after-tax or $0.00 per diluted share). Also includes $2.0 million of income tax benefit for the re-measurement of our net deferred tax liability to our 2017 measurement period adjustments in accordance with SEC Staff Accounting Bulletin No. 118 (SAB 118), Income Tax Accounting Implications of the Tax Cuts and Jobs Act ($0.02 per diluted share).

[5] Includes $4.0 million of charges related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($2.9 million after-tax or $0.04 per diluted share) and $1.3 million of charges consisting of closure costs related to corrugated products facilities and a corporate administration facility ($1.0 million after-tax or $0.01 per diluted share). Also includes $0.5 million of costs for the property damage insurance deductible for a weather-related incident at one of the corrugated products facilities ($0.4 million after-tax or $0.00 per diluted share) and $0.1 million of charges for acquisition and integration costs related to recent acquisitions ($0.01 million after-tax or $0.00 per diluted share).

[6] Includes $0.2 million of charges consisting of closure costs related to corrugated products facilities and a corporate administration facility ($0.2 million after-tax and $0.00 per diluted share) and $13.6 million of charges related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($10.2 million after-tax or $0.11 per diluted share).

[7] Includes $0.3 million of charges consisting of closure costs related to corrugated products facilities and a corporate administration facility ($0.2 million after-tax or $0.00 per diluted share) and $8.8 million of charges related to the second quarter 2018 discontinuation of uncoated free sheet and coated one-side white paper grades at the Wallula Washington mill associated with the conversion of the No. 3 paper machine to produce virgin kraft linerboard ($6.6 million after-tax or $0.07 per diluted share).

[8] 2017 has not been adjusted under the modified retrospective method for Topic 606.