Earnings Per Share - Computation of Basic and Diluted Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018	[1]	Sep. 30, 2018	[2]	Jun. 30, 2018	[3]	Mar. 31, 2018	[4]	Dec. 31, 2017	[5]	Sep. 30, 2017	[6]	Jun. 30, 2017	[7]	Mar. 31, 2017	[8]	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 204.6		$ 206.7		$ 186.6		$ 140.1		$ 268.9		$ 139.1		$ 143.2		$ 117.4		$ 738.0	$ 668.6	$ 449.6
Less: distributed and undistributed earnings allocated to participating securities																	(5.7)	(5.6)	(4.4)
Net income attributable to common stockholders																	$ 732.3	$ 663.0	$ 445.2
Denominator:
Weighted average common shares outstanding (in shares)																	93.7	93.5	93.5
Effect of dilutive securities (in shares)																	0.2	0.2	0.2
Diluted common shares outstanding (in shares)																	93.9	93.7	93.7
Basic income per common share (in dollars per share)	$ 2.17		$ 2.19		$ 1.98		$ 1.48		$ 2.85		$ 1.47		$ 1.52		$ 1.25		$ 7.82	$ 7.09	$ 4.76
Diluted income per common share (in dollars per share)	$ 2.16		$ 2.18		$ 1.97		$ 1.48		$ 2.84		$ 1.47		$ 1.52		$ 1.24		$ 7.80	$ 7.07	$ 4.75

[1] Includes $3.6 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 a high-performance 100% virgin kraft linerboard machine ($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 $0.0 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).

[2] Includes $4.0 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 ($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 $0.0 per diluted share) and $0.1 million of charges for acquisition and integration costs related to recent acquisitions ($0.01 million after-tax or $0.0 per diluted share).

[3] 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 $0.0 per diluted share) and $13.6 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 a high-performance 100% virgin kraft linerboard machine ($10.2 million after-tax or $0.11 per diluted share).

[4] 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 $0.0 per diluted share) and $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 ($6.6 million after-tax or $0.07 per diluted share).

[5] Includes $7.6 million of income 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, a paper administration facility, and a corporate administration facility ($4.7 million after-tax or $0.05 per diluted share) and $0.9 million of charges for acquisition and integration costs related to recent acquisitions ($0.5 million after-tax or $0.01 per diluted share), and $8.0 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 ($4.6 million after-tax or $0.05 per diluted share). Also includes $1.8 million of expense related to the write-off of deferred debt issuance costs in connection with the December 2017 debt refinancing ($1.1 million after-tax or $0.01 per diluted share), $2.0 million gain related to the expiration of a repurchase option corresponding to timberland previously sold ($1.2 million after-tax or $0.01 per diluted share), and $122.1 million of estimated income tax benefit related to the enactment in December 2017 of the Tax Cuts and Jobs Act (H.R.1) primarily for the re-measurement of our net deferred tax liability as a result of the reduction in the U.S. corporate income tax rate ($1.29 per diluted share).

[6] Includes $0.9 million of charges related to the closure of corrugated products facilities, a paper administration facility, and a lump sum settlement of a multiemployer pension plan withdrawal liability for one of our corrugated products facilities ($0.6 million after-tax or $0.01 per diluted share) and $0.5 million of charges for acquisition and integration costs related to recent acquisitions ($0.3 million after-tax or $0.0 per diluted share). Also includes $25.3 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 ($15.5 million after-tax or $0.16 per diluted share) and $3.3 million of tax expense for the change in value of deferred taxes as a result of an internal legal entity consolidation that will simplify future operating activities ($0.04 per diluted share).

[7] Includes $0.3 million of charges related to the closure of corrugated products facilities ($0.3 million after-tax or $0.0 per diluted share) and $0.2 million of charges for integration costs related to recent acquisitions ($0.1 after-tax or $0.0 per diluted share).

[8] Includes $0.6 million of charges related to the closure of corrugated products facilities and lump sum settlement of a multiemployer pension plan withdrawal liability for one of corrugated products facilities ($0.4 million after-tax or $0.01 per diluted share) and $0.2 million of charges for integration costs related to recent acquisitions ($0.1 million after-tax or $0.0 per diluted share). Also includes $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 ($3.1 million after-tax or $0.03 per diluted share) and $2.3 million of income related to a working capital adjustment from the April 2015 sale of our Hexacomb corrugated manufacturing operations in Europe and Mexico ($1.4 million after-tax or $0.01 per diluted share).