Segment Information - Analysis of Operations by Reportable Segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended															12 Months Ended						3 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Segment Reporting Information [Line Items]
Trade sales																$ 5,852.6		$ 3,665.3	[1]	$ 2,843.9
Net sales	1,434.0	[2]	1,518.9	[3]	1,468.4	[4]	1,431.3	[5]	1,264.4	[6]	845.5	[7]	800.2	[8]	755.2	5,852.6		3,665.3		2,843.9
Operating Income (Loss)	173.2	[2]	188.4	[3]	180.2	[4]	160.9	[5]	122.9	[6]	142.8	[7]	110.2	[8]	106.0	702.7		481.9	[1]	437.6
Interest expense, net																(88.4)	[9]	(58.3)	[1],[10]	(62.9)	[11]
Income before taxes																614.3		423.6	[1]	374.7
Depreciation, amortization, and depletion																381.0		201.8	[1]	170.8
Capital expenditures																420.2	[12]	234.4	[1],[12]	128.5	[12]
Assets	5,348.5								5,243.8	[1]						5,348.5		5,243.8	[1]	2,494.9
Class action lawsuit settlement																17.6	[13]	0		0
Write-Off of Deferred Financing Costs
Segment Reporting Information [Line Items]
Interest expense, net																(1.5)
Packaging
Segment Reporting Information [Line Items]
Trade sales																4,534.5		3,431.3	[1]	2,843.9
Operating Income (Loss)																663.2	[14]	554.2	[1],[15]	383.9	[16]
Depreciation, amortization, and depletion																323.0		190.2	[1]	169.4
Capital expenditures																362.1	[12]	222.2	[1],[12]	127.8	[12]
Assets	4,105.3								3,988.5	[1]						4,105.3		3,988.5	[1]	2,194.5
Paper
Segment Reporting Information [Line Items]
Trade sales																1,201.4		216.9	[1]
Operating Income (Loss)																135.4		13.5	[1],[17]
Depreciation, amortization, and depletion																50.6		9.1	[1]
Capital expenditures																51.7	[12]	10.0	[1],[12]
Assets	968.6								938.4	[1]						968.6		938.4	[1]
Corporate and Other
Segment Reporting Information [Line Items]
Trade sales																116.7		17.1	[1]	0
Operating Income (Loss)																(95.9)	[18]	(85.8)	[1],[19]	53.7	[20]
Depreciation, amortization, and depletion																7.4		2.5	[1]	1.4
Capital expenditures																6.4	[12]	2.2	[1],[12]	0.7	[12]
Assets	274.6								316.9	[1]						274.6		316.9	[1]	300.4
Class action lawsuit settlement																17.6
DeRidder Restructuring Costs
Segment Reporting Information [Line Items]
Operating Income (Loss)	(18.0)		(26.0)		(17.8)		(4.0)
Acquisition Inventory Step-Up | Boise Inc.
Segment Reporting Information [Line Items]
Operating Income (Loss)									21.5
Acquisition Inventory Step-Up | Boise Inc. | Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																		(18.0)
Acquisition Inventory Step-Up | Boise Inc. | Paper
Segment Reporting Information [Line Items]
Operating Income (Loss)																		(3.5)
Integration-Related and Other Costs | Boise Inc.
Segment Reporting Information [Line Items]
Operating Income (Loss)	(6.4)				(4.9)		(4.1)		(17.4)
Income before taxes			(4.5)
Integration-Related and Other Costs | Boise Inc. | Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																		(1.4)
Integration-Related and Other Costs | Boise Inc. | Paper
Segment Reporting Information [Line Items]
Operating Income (Loss)																		1.9
Integration-Related and Other Costs | Boise Inc. | Corporate and Other
Segment Reporting Information [Line Items]
Operating Income (Loss)																		(17.9)
Nonrecurring Acquisition-Related Costs | Boise Inc.
Segment Reporting Information [Line Items]
Operating Income (Loss)									(15.8)		(1.5)
Nonrecurring Acquisition-Related Costs | Boise Inc. | Corporate and Other
Segment Reporting Information [Line Items]
Operating Income (Loss)																		(17.2)
Acquisition-Related Debt Financing Costs | Boise Inc.
Segment Reporting Information [Line Items]
Interest expense, net									(8.9)		(2.7)
Acquisition-Related Debt Financing Costs | Boise Inc. | Acquisition Financing Expense
Segment Reporting Information [Line Items]
Interest expense, net																		(10.5)
Acquisition-Related Debt Financing Costs | Boise Inc. | Write-Off of Deferred Financing Costs
Segment Reporting Information [Line Items]
Interest expense, net																		(1.1)
Plant Closure | Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																				(2.0)
Debt Refinancing Charges
Segment Reporting Information [Line Items]
Interest expense, net																				(24.8)
Debt Refinancing Charges | Redemption Premium
Segment Reporting Information [Line Items]
Interest expense, net																				(21.3)
Debt Refinancing Charges | Treasury Lock
Segment Reporting Information [Line Items]
Interest expense, net																				(3.4)
Debt Refinancing Charges | Other Debt Refinancing Charges
Segment Reporting Information [Line Items]
Interest expense, net																				(0.1)
Alternative Energy Tax Credits | Corporate and Other
Segment Reporting Information [Line Items]
Alternative energy tax credits																						95.5
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment sales																0		0	[1]	0
Intersegment Eliminations | Packaging
Segment Reporting Information [Line Items]
Intersegment sales																5.8		0.4	[1]	0
Intersegment Eliminations | Paper
Segment Reporting Information [Line Items]
Intersegment sales																0		0	[1]
Intersegment Eliminations | Corporate and Other
Segment Reporting Information [Line Items]
Intersegment sales																144.9		28.0	[1]	0
Operating Segments
Segment Reporting Information [Line Items]
Net sales																5,852.6		3,665.3	[1]	2,843.9
Operating Segments | Packaging
Segment Reporting Information [Line Items]
Net sales																4,540.3		3,431.7	[1]	2,843.9
Operating Segments | Paper
Segment Reporting Information [Line Items]
Net sales																1,201.4		216.9	[1]	0
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
Net sales																261.6		45.1	[1]	0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Intersegment sales																(150.7)		(28.4)	[1]
Net sales																(150.7)		(28.4)	[1]
Other Expense | DeRidder Restructuring Costs | Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																(65.8)
Other Expense | Integration-Related and Other Costs | Boise Inc. | Packaging
Segment Reporting Information [Line Items]
Operating Income (Loss)																(4.9)
Other Expense | Integration-Related and Other Costs | Boise Inc. | Corporate and Other
Segment Reporting Information [Line Items]
Operating Income (Loss)																$ (13.5)

[1] On October 25, 2013, we acquired Boise Inc. (Boise). Our financial results include Boise subsequent to acquisition.

[2] Includes $18.0 million of DeRidder restructuring charges ($11.7 million after-tax or $0.12 per diluted share) and $6.4 million of integration-related and other costs ($4.2 million after-tax or $0.04 per diluted share).

[3] Includes $26.0 million of DeRidder restructuring charges ($16.6 million after-tax or $0.17 per diluted share) and $4.5 million of integration-related and other costs ($2.9 million after-tax or $0.03 per diluted share).

[4] Includes $17.8 million of DeRidder restructuring charges ($11.2 million after-tax or $0.12 per diluted share) and $4.9 million of integration-related and other costs ($3.0 million after-tax or $0.03 per diluted share).

[5] Includes $17.6 million of costs accrued for the settlement of the Kleen Products LLC v Packaging Corp. of America et al class action lawsuit ($11.2 million after-tax or $0.11 per diluted share), $4.1 million of integration-related costs ($2.6 million after-tax or $0.03 per diluted share), and $4.0 million of DeRidder restructuring charges ($2.6 million after-tax or $0.02 per diluted share).

[6] Includes Boise's results for the period of October 25, 2013, through December 31, 2013. The quarter also includes $166.0 million of income tax benefits from the reversal of the reserves for unrecognized tax benefits from alternative energy tax credits ($1.70 per diluted share), partially offset by $21.5 million of expense for the acquisition inventory step-up ($13.6 million after-tax or $0.14 per diluted share), $15.8 million of acquisition-related costs ($10.0 million after-tax or $0.10 per diluted share), $8.9 million of acquisition-related financing costs ($5.6 million after-tax or $0.06 per diluted share), and $17.4 million of integration-related and other costs ($11.0 million after-tax or $0.11 per diluted share).

[7] Includes a $3.1 million non-cash pension curtailment charge ($2.0 million after-tax or $0.02 per diluted share), $1.5 million of acquisition-related costs ($1.0 million after-tax or $0.01 per diluted share), and $2.7 million of acquisition-related financing costs ($1.8 million after-tax or $0.02 per diluted share).

[8] Includes a $7.8 million non-cash pension curtailment charge ($5.0 million after-tax or $0.05 per diluted share).

[9] Includes $1.5 million of expense related to the write-off of deferred financing costs in connection with the debt refinancing discussed in Note 10, Debt.

[10] Includes $10.5 million of expenses for financing the acquisition and $1.1 million of expense for the write-off of deferred financing costs.

[11] Includes $24.8 million of debt refinancing charges, including a $21.3 million redemption premium, a $3.4 million charge to settle the treasury lock prior to its maturity, and $0.1 million of other items.

[12] 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.

[13] Includes $17.6 million of costs for the settlement of the Kleen Products LLC v Packaging Corp. of America et al class action lawsuit. See Note 20, Commitments, Guarantees, Indemnifications, and Legal Proceedings, for more information.

[14] Includes $65.8 million of costs related primarily to the conversion of the No. 3 newsprint machine at our DeRidder, Louisiana, mill to produce lightweight linerboard and corrugating medium, and our exit from the newsprint business in September 2014. Includes $4.9 million of Boise acquisition integration-related and other costs, most of which are recorded in "Other expense, net".

[15] Includes $18.0 million of expense for the acquisition inventory step-up and $1.4 million of integration-related and other costs incurred in connection with the acquisition of Boise in fourth quarter 2013.

[16] Includes $2.0 million of plant closure charges.

[17] Includes $3.5 million of expense for acquisition inventory step-up and $1.9 million of income for integration-related and other costs.

[18] Includes $13.5 million of Boise acquisition integration-related and other costs, most of which are recorded in "Other expense, net". Includes $17.6 million of costs for the settlement of the Kleen Products LLC v Packaging Corp. of America et al class action lawsuit recorded in "Other expense, net". See Note 20, Commitments, Guarantees, Indemnifications, and Legal Proceedings, for more information.

[19] Includes $17.2 million of acquisition-related costs and $17.9 million of integration-related and other costs.

[20] Includes $95.5 million of income related to the increase in gallons claimed as alternative energy tax credits on the Company's amended 2009 tax return. See Note 7, Alternative Energy Tax Credits, for more information.