Segment Information - Analysis of Operations by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended															12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019	[2]	Jun. 30, 2019	Mar. 31, 2019	[3]	Dec. 31, 2018		Sep. 30, 2018	[5]	Jun. 30, 2018	[6]	Mar. 31, 2018	[7]	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ 235.1	[1]	$ 262.8		$ 280.4	$ 275.4		$ 286.7	[4]	$ 298.5		$ 269.6		$ 212.9		$ 1,053.7		$ 1,067.7		$ 932.5	[8]
Net sales	1,720.0	[1]	$ 1,750.7		$ 1,759.9	$ 1,733.7		1,746.6	[4]	$ 1,809.9		$ 1,767.5		$ 1,690.6		6,964.3		7,014.6		6,444.9	[9]
Non-operating pension expense																(7.9)		(2.1)		(1.3)	[8]
Interest expense, net																(128.8)	[10]	(95.1)		(102.6)	[8],[11]
Income before taxes																917.0		970.5		828.6	[8]
Depreciation, Amortization, and Depletion																387.5		410.9		391.4
Capital Expenditures																399.5	[8]	551.4	[8]	343.0
Assets	7,235.8							6,569.7								7,235.8		6,569.7		6,197.5
Trade
Segment Reporting Information [Line Items]
Net sales																6,964.3		7,014.6		6,444.9
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales																(160.2)		(155.6)		(148.4)
Operating Segments
Segment Reporting Information [Line Items]
Net sales																6,964.3		7,014.6		6,444.9
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales																(160.2)		(155.6)		(148.4)
Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																963.4	[12]	1,045.4	[13]	950.3	[8],[14]
Net sales																5,932.2		5,938.5		5,312.3	[9]
Depreciation, Amortization, and Depletion																342.8		342.0		317.5
Capital Expenditures																367.4	[8]	504.0	[8]	305.1
Assets	5,491.5							5,347.0								5,491.5		5,347.0		4,933.6
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales																5,905.1		5,912.3		5,288.6
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales																27.1		26.2		23.7
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales																5,932.2		5,938.5		5,312.3
Paper
Segment Reporting Information [Line Items]
Operating Income (Loss)																175.4	[15]	97.7	[16]	54.0	[8],[17]
Net sales																964.3		1,002.0		1,051.8	[9]
Depreciation, Amortization, and Depletion																37.7		62.0		67.6
Capital Expenditures																23.8	[8]	12.6	[8]	22.6
Assets	791.4							760.1								791.4		760.1		945.2
Paper | Trade
Segment Reporting Information [Line Items]
Net sales																964.3		1,002.0		1,051.8
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales																964.3		1,002.0		1,051.8
Corporate and Other
Segment Reporting Information [Line Items]
Operating Income (Loss)																(85.1)		(75.4)	[18]	(71.8)	[8],[19]
Net sales																67.8		74.1		80.8	[9]
Depreciation, Amortization, and Depletion																7.0		6.9		6.3
Capital Expenditures																8.3	[8]	34.8	[8]	15.3
Assets	$ 952.9							$ 462.6								952.9		462.6		318.7
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales																94.9		100.3		104.5
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales																133.1		129.4		124.7
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales																$ 228.0		$ 229.7		$ 229.2

[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] Includes “Additions to property, plant, and equipment” and excludes cash used for “Acquisitions of businesses, net of cash acquired” as reported on our Consolidated Statements of Cash Flows.

[9] 2017 has not been adjusted under the modified retrospective method for Topic 606.

[10] Includes $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.

[11] Includes $1.8 million of expense related to the write-off of deferred debt issuance costs in connection with the December 2017 debt refinancing.

[12] (b)     Includes the following:   o $3.0 million of charges for the disposal of fixed assets related to the containerboard mill conversion at our DeRidder, Louisiana mill.   o $0.8 million of charges related to the second quarter 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.   o $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.

[13] (e)     Includes the following:   o $12.3 million of charges related to the second quarter 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.   o $1.6 million of charges consisting of closure costs related to corrugated products facilities.   o $0.5 million of costs for the property damage insurance deductible for a weather-related incident at one of the corrugated products facilities.   o $0.2 million of charges for acquisition and integration costs related to recent acquisitions.

[14] (h)     Includes the following:   o $7.2 million of income, net, primarily related to the sale of land corresponding to the closure of a corrugated products facility, partially offset by closure costs related to corrugated products facilities, and a lump sum settlement of a multiemployer pension plan withdrawal liability for one of our corrugated products facilities.   o $1.7 million of charges for acquisition and integration costs related to recent acquisitions.   o $2.0 million gain related to the expiration of a repurchase option corresponding to timberland previously sold.   o $1.6 million of income related to a working capital adjustment from the April 2015 sale of our Hexacomb corrugated manufacturing operations in Europe and Mexico.   o $5.0 million of costs for the property damage and business interruption insurance deductible corresponding to the February 2017 explosion at our DeRidder, Louisiana mill.

[15] Includes $0.2 million of charges related to the second quarter 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.

[16] Includes $17.7 million of charges related to the second quarter 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.

[17] Includes $33.4 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 and $0.4 million of charges related to the closure costs of a paper administration facility.

[18] Includes $0.2 million of charges consisting of closure costs related to a corporate administration facility.

[19] Includes $1.0 million of charges related to the closure costs of a corporate administration facility and $0.7 million of income related to a working capital adjustment from the April 2015 sale of our Hexacomb corrugated manufacturing operations in Europe and Mexico.