Packaging Corporation of America (PKG) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Registrant Name	PACKAGING CORP OF AMERICA
Entity Central Index Key	0000075677
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		94,990,766
Entity File Number	1-15399
Entity Tax Identification Number	36-4277050
Entity Address, Address Line One	1 North Field Court
Entity Address, City or Town	Lake Forest
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60045
City Area Code	847
Local Phone Number	482-3000
Document Quarterly Report	true
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	PKG
Security Exchange Name	NYSE

Consolidated Statements of Inco

Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Net sales	$ 2,000.1	$ 1,693.7	$ 5,687.1	$ 4,944
Cost of sales	(1,489.4)	(1,348.3)	(4,324)	(3,907.9)
Gross profit	510.7	345.4	1,363.1	1,036.1
Selling, general and administrative expenses	(144.5)	(127.1)	(435.7)	(409.3)
Goodwill impairment	0	0	0	(55.2)
Other expense, net	(13.4)	(8.8)	(41.7)	(36.9)
Income from operations	352.8	209.5	885.7	534.7
Non-operating pension income	5	0.6	14.8	1.7
Interest expense, net	(23.9)	(24.4)	(72.2)	(69.1)
Income before taxes	333.9	185.7	828.3	467.3
Provision for income taxes	(83.2)	(46.6)	(203.7)	(129.9)
Net income	$ 250.7	$ 139.1	$ 624.6	$ 337.4
Net income per common share:
Basic	$ 2.64	$ 1.47	$ 6.58	$ 3.56
Diluted	2.63	1.46	6.55	3.54
Dividends declared per common share	$ 1	$ 0.79	$ 3	$ 2.37
Statements of Comprehensive Income:
Net income	$ 250.7	$ 139.1	$ 624.6	$ 337.4
Foreign currency translation adjustment	0.4	0	0.4	0
Changes in unrealized gains (losses) on marketable debt securities, net of tax of $0.0 million, $0.1 million, $0.1 million, and $0.2 million	0	(0.2)	(0.2)	0.5
Amortization of pension and postretirement plans actuarial loss and prior service cost, net of tax of $0.8 million, $0.9 million, $2.5 million, and $2.7 million	2.5	2.7	7.5	8.1
Other comprehensive income	2.9	2.5	7.7	8.6
Comprehensive income	$ 253.6	$ 141.6	$ 632.3	$ 346

Consolidated Statements of In_2

Consolidated Statements of Income and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Changes in unrealized losses on marketable debt securities, tax	$ 0	$ 0.1	$ 0.1	$ 0.2
Amortization of pension and postretirement plans actuarial loss and prior service cost, tax	$ 0.8	$ 0.9	$ 2.5	$ 2.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2021		Dec. 31, 2020
Current assets:
Cash and cash equivalents		$ 1,702.9	[1]	$ 974.6
Short-term marketable debt securities		88.3	[1]	105.6
Accounts receivable, net of allowance for credit losses and customer deductions of $15.1 million and $10.6 million as of September 30, 2021 and December 31, 2020, respectively		1,066.7		832.4
Inventories		880.1		787.9
Prepaid expenses and other current assets		55.4		44.7
Federal and state income taxes receivable		11.4		5.1
Total current assets		3,804.8		2,750.3
Property, plant, and equipment, net		3,360.8		3,193.4
Goodwill		863.5		863.5
Other intangible assets, net		267.7		295.9
Operating lease right-of-use assets		230.4		234.2
Long-term marketable debt securities		57.8	[1]	42.7
Other long-term assets		45.8		53.2
Total assets		8,630.8		7,433.2
Current liabilities:
Current maturities of long-term debt	[2]	698.1		0
Operating lease obligations		67.2		68.9
Finance lease obligations		1.7		1.6
Accounts payable		499.1		387
Dividends payable		97.3		97
Accrued liabilities		252.5		216.2
Accrued interest		28.5		11.9
Total current liabilities		1,644.4		782.6
Long-term liabilities:
Long-term debt		2,471.1		2,479.4
Operating lease obligations		171.5		173.6
Finance lease obligations		13.1		14.4
Deferred income taxes		423.9		379.4
Compensation and benefits		241.1		298.3
Other long-term liabilities		57.4		59.2
Total long-term liabilities		3,378.1		3,404.3
Commitments and contingent liabilities
Stockholders' equity:
Common stock, par value $0.01 per share, 300.0 million shares authorized, 95.0 million and 94.8 million shares issued as of September 30, 2021 and December 31, 2020, respectively		1		0.9
Additional paid in capital		581.3		554.4
Retained earnings		3,162.8		2,835.5
Accumulated other comprehensive loss		(136.8)		(144.5)
Total stockholders' equity		3,608.3		3,246.3
Total liabilities and stockholders' equity		$ 8,630.8		$ 7,433.2
[1]	Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.
[2]	The current portion of long-term debt excludes unamortized debt issuance costs of $ 1.4 million at September 30, 2021.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Allowance for credit losses and customer deductions	$ 15.1	$ 10.6
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	95,000,000	94,800,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities:
Net income	$ 624.6	$ 337.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization of intangibles	311.1	309
Amortization of deferred financing costs	2	1.9
Share-based compensation expense	26.9	23.8
Deferred income tax provision	41.7	21.1
Loss on asset disposals	7.3	4.1
Goodwill impairment	0	55.2
Pension and post-retirement benefits expense, net of contributions	(50.4)	(68.1)
Other, net	8.9	18.8
(Increase) decrease in assets -
Accounts receivable	(234.3)	(19)
Inventories	(92.3)	16.5
Prepaid expenses and other current assets	(11.8)	(5.6)
Increase (decrease) in liabilities -
Accounts payable	22.3	(6.2)
Accrued liabilities	53.5	29
Federal and state income taxes payable / receivable	(6.1)	43.8
Net cash provided by operating activities	703.4	761.7
Cash Flows from Investing Activities:
Additions to property, plant, and equipment	(366.2)	(253.5)
Additions to other long term assets	(1.8)	(6.2)
Proceeds from asset disposals	2.6	4.4
Purchases of marketable debt securities	(100.3)	(71.5)
Proceeds from sales of marketable debt securities	17.7	17.2
Proceeds from maturities of marketable debt securities	83	53.7
Net cash used for investing activities	(365)	(255.9)
Cash Flows from Financing Activities:
Repayments of debt and finance lease obligations	(1.2)	(1.1)
Proceeds from issuance of debt	696.3	0
Financing costs paid	(8.5)	0
Common stock dividends paid	(284.8)	(224.6)
Shares withheld to cover employee restricted stock taxes	(11.9)	(10.5)
Net cash provided by (used for) financing activities	389.9	(236.2)
Net increase in cash and cash equivalents	728.3	269.6
Cash and cash equivalents, beginning of period	974.6	679.5
Cash and cash equivalents, end of period	$ 1,702.9	$ 949.1

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2019	$ 3,071	$ 0.9	$ 524.8	$ 2,704.8	$ (159.5)
Beginning Balance (in shares) at Dec. 31, 2019		94,655
Common stock withheld and retired to cover taxes on vested stock awards	(10.5)	$ 0	(0.8)	(9.7)	0
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(108)
Common stock dividends declared	(225.8)	$ 0	0	(225.8)	0
Share-based compensation and other	24.7	$ 0	24.7	0	0
Share-based compensation expense (in shares)		284
Comprehensive income	346	$ 0	0	337.4	8.6
Ending Balance at Sep. 30, 2020	3,205.4	$ 0.9	548.7	2,806.7	(150.9)
Ending Balance (in shares) at Sep. 30, 2020		94,831
Beginning Balance at Jun. 30, 2020	3,133.1	$ 0.9	542.7	2,742.9	(153.4)
Beginning Balance (in shares) at Jun. 30, 2020		94,835
Common stock withheld and retired to cover taxes on vested stock awards	(0.1)	$ 0	0	(0.1)	0
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(1,000)
Common stock dividends declared	(75.2)	$ 0	0	(75.2)	0
Share-based compensation and other	6	$ 0	6	0	0
Share-based compensation expense (in shares)		3
Comprehensive income	141.6	$ 0	0	139.1	2.5
Ending Balance at Sep. 30, 2020	3,205.4	$ 0.9	548.7	2,806.7	(150.9)
Ending Balance (in shares) at Sep. 30, 2020		94,831
Beginning Balance at Dec. 31, 2020	3,246.3	$ 0.9	554.4	2,835.5	(144.5)
Beginning Balance (in shares) at Dec. 31, 2020		94,830
Common stock withheld and retired to cover taxes on vested stock awards	(12)	$ (0.1)	(0.7)	(11.2)	0
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(88)
Common stock dividends declared	(286.2)	$ 0	0	(286.2)	0
Share-based compensation and other	27.9	$ 0.2	27.6	0.1	0
Share-based compensation expense (in shares)		249
Comprehensive income	632.3	$ 0	0	624.6	7.7
Ending Balance at Sep. 30, 2021	3,608.3	$ 1	581.3	3,162.8	(136.8)
Ending Balance (in shares) at Sep. 30, 2021		94,991
Beginning Balance at Jun. 30, 2021	3,444.3	$ 1	574.5	3,008.5	(139.7)
Beginning Balance (in shares) at Jun. 30, 2021		94,979
Common stock withheld and retired to cover taxes on vested stock awards	(1.4)	$ 0	(0.1)	(1.3)	0
Common stock withheld and retired to cover taxes on vested stock awards (in shares)		(10)
Common stock dividends declared	(95.3)	$ 0	0	(95.3)	0
Share-based compensation and other	7.1	$ 0	6.9	0.2	0
Share-based compensation expense (in shares)		22
Comprehensive income	253.6	$ 0	0	250.7	2.9
Ending Balance at Sep. 30, 2021	$ 3,608.3	$ 1	$ 581.3	$ 3,162.8	$ (136.8)
Ending Balance (in shares) at Sep. 30, 2021		94,991

Nature of Operations and Basis

Nature of Operations and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Basis of Presentation	1. Nature of Operations and Basis of Presentation Packaging Corporation of America ("we," "us," "our," PCA," or the "Company") was incorporated on January 25, 1999 . In April 1999, PCA acquired the containerboard and corrugated packaging products business of Pactiv Corporation (Pactiv), formerly known as Tenneco Packaging, Inc. We are a large diverse manufacturer of both packaging and paper products. We are headquartered in Lake Forest, Illinois and we operate primarily in the United States. We report our business in three reportable segments: Packaging, Paper, and Corporate and Other. Our Packaging segment produces a wide variety of containerboard and corrugated packaging products. The Paper segment manufactures and sells a range of communication-based papers. Corporate and Other includes support staff services and related assets and liabilities, transportation assets, and activity related to other ancillary support operations. For more information about our segments, see Note 18, Segment Information. During the fourth quarter of 2020, in order to meet strong packaging demand and maintain appropriate inventory levels, we temporarily began producing linerboard on the No. 3 machine at our Jackson, Alabama mill. In the first quarter of 2021, we announced the discontinuation of production of uncoated freesheet paper grades on the machine and the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. Before October 2020, operating results for the Jackson mill were included in the Paper segment. Beginning in October 2020, operating results for the Jackson mill are included in both the Packaging and Paper segments. In these consolidated financial statements, certain amounts in prior periods’ consolidated financial statements have been reclassified to conform with the current period presentation. The consolidated financial statements of PCA as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 are unaudited but include all adjustments (consisting only of normal recurring adjustments) that management considers necessary for a fair presentation of such financial statements. The preparation of the consolidated financial statements involves the use of estimates and accruals. Actual results may vary from those estimates. These financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and notes required by accounting principles generally accepted in the United States for complete audited financial statements. Operating results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. These consolidated financial statements should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2020. The consolidated financial statements include the accounts of PCA and its majority-owned subsidiaries after elimination of intercompany balances and transactions.

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
New Accounting Standards	2. New Accounting Standards In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting. ASU 2020-04 provides optional guidance for a limited period of time to ease the potential burden in accounting for, or recognizing the effects of, reference rate reform on financial reporting. The amendments in this Update are elective and apply to all entities, subject to meeting certain criteria, that have contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. In January 2021, the FASB issued ASU 2021-01, which extends some of the optional expedients under Topic 848 to include derivative contracts impacted by discounting transition. Companies can apply the ASU immediately. The ASU can be adopted on a full retrospective basis as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or on a prospective basis to any new modification from any date within an interim period that includes or is subsequent to the date of the issuance of a final Update, up to the date that financial statements are available to be issued. The optional guidance will only be available until December 31, 2022. While the Company’s fixed-rate outstanding debt will not be impacted by the reference rate reform, the Company is still evaluating the impact of this guidance on its revolving credit facility, as the interest rate associated with any future borrowings against the revolving credit facility is based on LIBOR. Overall, the Company does not expect the guidance to have a significant impact on its financial position or related disclosures. There were no other accounting standards recently issued that had or are expected to have a material impact on our financial position or results of operations.

Revenue

Revenue	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	3. Revenue Revenue Recognition Revenue is recognized when control of the promised goods or services is transferred to customers in an amount that reflects the consideration expected to be received in exchange for those goods or services. Sales, value added, and other taxes collected concurrently with revenue-producing activities are excluded from revenue. The following table presents our revenues disaggregated by product line (dollars in millions): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Packaging $ 1,829.4 $ 1,501.1 $ 5,171.4 $ 4,378.5 Paper 150.3 178.1 457.1 518.7 Corporate and Other 20.4 14.5 58.6 46.8 Total revenue $ 2,000.1 $ 1,693.7 $ 5,687.1 $ 4,944.0 Packaging Revenue Our containerboard mills produce linerboard and corrugating medium which are papers primarily used in the production of corrugated products. The majority of our containerboard production is used internally by our corrugated products manufacturing facilities. The remaining containerboard is sold to outside domestic and export customers. Our corrugated products manufacturing plants produce a wide variety of corrugated packaging products and retail merchandise displays. We sell corrugated products to national, regional and local accounts, which are broadly diversified across industries and geographic locations. The Company recognizes revenue for its packaging products when performance obligations under the terms of a contract with a customer are satisfied. This occurs with the transfer of control of our products at a specific point in time. Based on our express terms and conditions of the sale of products to our customers, as well as terms included in contractual arrangements with our customers, we do not have an enforceable right of payment that includes a reasonable profit throughout the duration of the contract for products that do not have an alternative use. Revenue is recognized when the product is shipped from the mill or from our manufacturing facility to our customer. Certain customers may receive volume-based incentives, which are accounted for as variable consideration. We estimate these amounts based on the expected amount to be provided to customers and reduce revenue recognized. Certain customers receive a portion of their packaging products as consigned inventory with billing triggered once the customer uses or consumes the designated product. Prior to invoicing, these amounts are handled as unbilled receivables. Total unbilled receivables, which are immaterial in amount, are included in the accounts receivable financial statement caption. Paper Revenue We manufacture and sell a range of communication-based papers. Communication papers consist of cut-size office papers, and printing and converting papers. The Company recognizes revenue for its paper products when performance obligations under the terms of a contract with a customer are satisfied. This occurs with the transfer of control of our products at a specific point in time. Revenue is recognized when the product is shipped from the mill or from our manufacturing facility or distribution center to our customer. Certain customers may receive volume-based incentives, which are accounted for as variable consideration. We estimate these amounts based on the expected amount to be provided to customers and reduce revenue recognized. Corporate and Other Revenue Revenue in this segment primarily relates to Louisiana Timber Procurement Company, L.L.C. (LTP), a variable-interest entity that is 50 % owned by PCA and 50 % owned by Boise Cascade Company (Boise Cascade). PCA is the primary beneficiary of LTP and has the power to direct the activities that most significantly affect the economic performance of LTP. Therefore, we consolidate 100% of LTP in our financial statements. See Note 17, Transactions With Related Parties, for more information related to LTP. The Company recognizes revenue within this segment when performance obligations under the terms of a contract with a customer are satisfied. This occurs with the transfer of control of our products at a specific point in time. Practical Expedients and Exemption Shipping and handling fees billed to a customer are recorded on a gross basis in "Net sales" with the corresponding shipping and handling costs included in "Cost of sales" in the concurrent period as the revenue is recorded. We expense sales commissions when incurred because the amortization period is one year or less. Sales commissions are recorded in "Selling, general, and administrative expenses". We do not disclose the value of unsatisfied performance obligations for contracts with an original expected duration of one year or less.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share	4. Earnings Per Share The following table sets forth the computation of basic and diluted income per common share for the periods presented (dollars and shares in millions, except per share data): Three Months Ended Nine Months Ended September 30, September 30, Numerator: 2021 2020 2021 2020 Net income $ 250.7 $ 139.1 $ 624.6 $ 337.4 Less: Distributed and undistributed earnings allocated to participating ( 1.7 ) ( 1.0 ) ( 4.9 ) ( 2.7 ) Net income attributable to common shareholders $ 249.0 $ 138.1 $ 619.7 $ 334.7 Denominator: Weighted average basic common shares outstanding 94.3 94.2 94.2 94.0 Effect of dilutive securities 0.4 0.3 0.4 0.4 Weighted average diluted common shares outstanding 94.7 94.5 94.6 94.4 Basic income per common share $ 2.64 $ 1.47 $ 6.58 $ 3.56 Diluted income per common share $ 2.63 $ 1.46 $ 6.55 $ 3.54

Other Expense, Net

Other Expense, Net	9 Months Ended
	Sep. 30, 2021
Other Income and Expenses [Abstract]
Other Expense, Net	5. Other Expense, Net The components of other income (expense), net, were as follows (dollars in millions): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Asset disposals and write-offs $ ( 6.4 ) $ ( 5.5 ) $ ( 27.3 ) $ ( 16.5 ) Jackson mill conversion-related activities (a) ( 3.2 ) — ( 6.1 ) — Facilities closure and other income (costs) (b) ( 0.7 ) ( 2.9 ) 2.7 ( 16.6 ) Other ( 3.1 ) ( 0.4 ) ( 11.0 ) ( 3.8 ) Total $ ( 13.4 ) $ ( 8.8 ) $ ( 41.7 ) $ ( 36.9 ) (a) Includes charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. (b) For the three months ended September 30, 2021, includes charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities, partially offset by closure costs related to corrugated products facilities. For 2020, includes costs primarily related to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	6. Income Taxes For the three months ended September 30, 2021 and 2020, we recorded $ 83.2 million and $ 46.6 million of income tax expense and had an effective tax rate of 24.9 % and 2 5.0 %, respectively. The decrease in our effective tax rate for the three months ended September 30, 2021 compared to the same period in 2020 was primarily due to the favorable state rate impact of a subsidiary merger during the three months ended September 30, 2021 compared to September 30, 2020. For the nine months ended September 30, 2021 and 2020, we recorded $ 203.7 million and $ 129.9 million of income tax expense and had an effective tax rate of 2 4.6 % and 27.8 %, respectively. The decrease in our effective tax rate for the nine months ended September 30, 2021 compared to the same period in 2020 was primarily due to the nondeductible goodwill impairment charge associated with our Paper reporting unit recognized during the nine months ended September 30, 2020 with no corresponding charge during the nine months ended September 30, 2021. Our current effective tax rate may differ from the federal statutory income tax rate of 21.0 % due primarily to the effect of state and local income taxes. During the nine months ended September 30, 2021 and 2020, cash paid for taxes, net of refunds received, was $ 168.1 million and $ 65.0 million, respectively. The increase in cash tax payments between the periods is primarily due to higher 2021 taxable income. During the three and nine months ended September 30, 2021, there were no significant changes to our uncertain tax positions. For more information, see Note 7, Income Taxes, of the Notes to Consolidated Financial Statements in “Part II, Item 8. Financial Statements and Supplementary Data” of our 2020 Annual Report on Form 10-K.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Inventories	7. Inventories We value our raw materials, work in process, and finished goods inventories using lower of cost, as determined by the average cost method, or net realizable value. Supplies and materials are valued at the first-in, first-out (FIFO) or average cost methods. The components of inventories were as follows (dollars in millions): September 30, December 31, 2021 2020 Raw materials $ 323.3 $ 263.5 Work in process 16.1 11.6 Finished goods 190.6 183.6 Supplies and materials 350.1 329.2 Inventories $ 880.1 $ 787.9

Property, Plant, and Equipment

Property, Plant, and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant, and Equipment	8. Property, Plant, and Equipment The components of property, plant, and equipment were as follows (dollars in millions): September 30, December 31, 2021 2020 Land and land improvements $ 186.2 $ 179.6 Buildings 895.5 858.5 Machinery and equipment 6,055.2 5,826.6 Construction in progress 417.5 360.0 Other 97.4 88.8 Property, plant and equipment, at cost 7,651.8 7,313.5 Less accumulated depreciation ( 4,291.0 ) ( 4,120.1 ) Property, plant, and equipment, net $ 3,360.8 $ 3,193.4 During the second quarter of 2020, with the exacerbated deterioration in uncoated freesheet market conditions arising from the COVID-19 pandemic and the estimated impact on our Paper segment and its projected future results of operations, we identified a triggering event indicating possible impairment of our long lived assets within our Paper segment, including property, plant, and equipment, and performed a recoverability test on the Paper reporting unit long lived assets as of May 31, 2020. The recoverability test was based on forecasts of undiscounted cash flows. The results of the recoverability test indicated that the long lived assets within our Paper segment, inclusive of property, plant, and equipment, were 100 % recoverable. Depreciation expense for the three months ended September 30, 2021 and 2020 was $ 95.5 million and $ 89.6 million, respectively. During the nine months ended September 30, 2021 and 2020, depreciation expense was $ 279.9 million and $ 272.7 million, respectively. We recognized $ 3.6 million of incremental depreciation expense during the nine months ended September 30, 2021 as a result of corrugated products facilities closures and the Jackson, Alabama mill conversion. We recognized $ 2.9 million of incremental depreciation expense during the nine months ended September 30, 2020 as a result of the closure of the San Lorenzo, California corrugated products facility. At September 30, 2021 and December 31, 2020, purchases of property, plant, and equipment included in accounts payable were $ 112.1 million and $ 22.2 million, respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	9. Goodwill and Intangible Assets During the second quarter of 2020, with the exacerbated deterioration in uncoated freesheet market conditions arising from the COVID-19 pandemic and the estimated impact on our Paper segment and its projected future results of operations, we identified a triggering event indicating possible impairment of goodwill and our long lived assets within our Paper reporting unit. Goodwill Due to the triggering event identified above an interim quantitative impairment analysis was performed as of May 31, 2020 for the Paper reporting unit, which is the same as our Paper reportable segment. We estimated the fair value of the Paper reporting unit using a combination of the income approach and the market approach, as further described below. Based on the evaluation performed, we determined that the carrying value of the Paper reporting unit exceeded its fair value, which resulted in a goodwill impairment charge totaling $ 55.2 million in the second quarter of 2020. For purposes of our goodwill impairment analysis, we estimated the fair value of the Paper reporting unit using a combination of the income approach and the market approach applying an equal weighting. The income approach incorporated the estimated future cash flows and a terminal value discounted to their present value using an appropriate risk-adjusted discount rate. The estimated future cash flows and terminal value were based on internal forecasts and industry trends, including the long-term outlook for the paper industry. Our expected cash flows include assumptions about industry pricing, expected paper demand, and anticipated input and conversion costs. The discount rate utilized in the income approach was 9 %, which was derived using a capital asset pricing model based on relevant industry data to estimate the cost of equity financing. The discount rate is commensurate with the risks and uncertainties inherent in the business and the cash flow forecasts, updated for recent events. The market approach estimated the fair value of the Paper reporting unit by using valuation metrics of publicly traded companies or historically completed transactions of comparable businesses. The valuation of our Paper reporting unit requires significant judgment in evaluating recent indicators of market activity and estimated future cash flows, discount rates, and other factors. Our impairment analysis contains inherent uncertainties due to uncontrollable events that could positively or negatively impact anticipated future economic and operating conditions. In making these estimates, the weighted-average cost of capital is utilized to calculate the present value of future cash flows and terminal value. Many variables go into estimating future cash flows, including estimates of our future revenue growth and operating results. When estimating our projected revenue growth and future operating results, we considered industry trends, economic data, and our competitive situation. Goodwill represents the excess of the cost of an acquired business over the fair value of the identifiable tangible and intangible assets acquired and liabilities assumed in a business combination. At both September 30, 2021 and December 31, 2020, we had $ 863.5 million of goodwill recorded in our Packaging segment, which represents the entire goodwill balance reported on our Consolidated Balance Sheets. Intangible Assets Intangible assets are primarily comprised of customer relationships and trademarks and trade names. As a result of the triggering event described above, we also performed a recoverability test on our long-lived assets within the Paper segment, including long lived intangible assets, as of May 31, 2020. The recoverability test was based on forecasts of undiscounted cash flows. The results of the recoverability test indicated that the long lived assets within our Paper segment, inclusive of the long lived intangible assets, were 100 % recoverable. The weighted average remaining useful life, gross carrying amount, and accumulated amortization of our intangible assets were as follows (dollars in millions): September 30, 2021 December 31, 2020 Weighted Gross Accumulated Weighted Gross Accumulated Customer relationships 8.4 $ 503.8 $ 246.2 9.1 $ 503.8 $ 220.2 Trademarks and trade names 9.3 34.8 24.8 9.3 34.8 23.0 Other 0.9 4.3 4.2 1.2 4.3 3.8 Total intangible assets (excluding goodwill) 8.5 $ 542.9 $ 275.2 9.1 $ 542.9 $ 247.0 During the nine months ended September 30, 2021 and 2020, amortization expense was $ 28.2 million and $ 33.4 million, respectively.

Accrued Liabilities

Accrued Liabilities	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities [Abstract]
Accrued Liabilities	10. Accrued Liabilities The components of accrued liabilities were as follows (dollars in millions): September 30, December 31, 2021 2020 Compensation and benefits $ 144.5 $ 126.5 Customer rebates and other credits 36.3 27.1 Medical insurance and workers’ compensation 26.5 25.5 Property, franchise, sales and use taxes 26.3 16.5 Environmental liabilities and asset retirement obligations 3.8 4.6 Severance, retention, and relocation 2.1 4.1 Other 13.0 11.9 Total $ 252.5 $ 216.2

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	11. Debt At September 30, 2021 and December 31, 2020, our long-term debt and interest rates on that debt were as follows (dollars in millions): September 30, December 31, 2021 2020 Revolving Credit Facility, due August 2021, terminated June 2021 $ — $ — Revolving Credit Facility, due June 2026 — — 4.50 % Senior Notes, net of discount of $ 0.5 million and 0.6 million as of September 30, 2021 and December 31, 2020, 699.5 699.4 3.65 % Senior Notes, net of discount of $ 0.4 million and 0.5 million as of September 30, 2021 and December 31, 2020, 399.6 399.5 3.40 % Senior Notes, net of discount of $ 1.1 million and 1.2 million as of September 30, 2021 and December 31, 2020, 498.9 498.8 3.00 % Senior Notes, net of discount of $ 0.5 million and 0.6 million as of September 30, 2021 and December 31, 2020, 499.5 499.4 4.05 % Senior Notes, net of discount of $ 3.4 million as of both 396.6 396.6 3.05 % Senior Notes, net of discount of $ 3.7 million as of October 2051 696.3 — Total 3,190.4 2,493.7 Less current portion (a) 698.1 — Less unamortized debt issuance costs 21.2 14.3 Total long-term debt $ 2,471.1 $ 2,479.4 (a) The current portion of long-term debt excludes unamortized debt issuance costs of $ 1.4 million at September 30, 2021. On September 21, 2021, the Company issued $ 700.0 million of 3.05 % senior notes due 2051 through a registered public offering, for the purpose of refinancing its $ 700.0 million of 4.50 % notes due November 1, 2023 . The old 4.50 % notes were subsequently redeemed on October 8, 2021. For the period ended September 30, 2021, PCA continued to record the normal amortization of the bond discount and debt issuance costs associated with the old 4.50 % notes. Although PCA communicated its intent to extinguish the old 4.50 % notes on September 8, 2021, the notes' corresponding liability was not deemed extinguished until the redemption occurred in October 2021, as required under Accounting Standards Codification (ASC) Topic 405, Liabilities - Extinguishments of Liabilities . Accordingly, as required under ASC Topic 470, Debt, the redemption premium associated with the old 4.50 % notes was not recognized until the extinguishment of the liability in October 2021. On October 8, 2021, PCA completed the redemption of the old 4.50 % notes for $ 769.8 million, which included a redemption premium of $ 56.1 million and $ 13.7 million of accrued and unpaid interest. The redemption of the old 4.50% notes also included a $ 1.4 million write-off of the remaining balance of unamortized debt issuance costs. PCA used the proceeds of the offering of the new 3.05 % notes and cash on hand to fund the redemption and the $ 7.6 million of debt issuance costs associated with the new notes. The debt issuance costs are amortized to interest expense using the effective interest method over the term of the notes. New Revolving Credit Agreement On June 8, 2021 , we entered into a revolving credit agreement with various financial institutions (the "New Revolving Credit Agreement"), which replaced the old Credit Agreement, dated August 29, 2016 (the "Old Credit Agreement"). The Old Credit Agreement was scheduled to terminate on August 29, 2021 . The New Revolving Credit Agreement is a $ 350 million unsecured revolving credit facility, which has a five-year term and is available for borrowings on a revolving basis for general corporate purposes. Except for approximately $ 23.5 million of letters of credit, no borrowings were outstanding under the Old Credit Agreement at the time of its replacement and no borrowings are outstanding under the New Revolving Credit Agreement. Borrowings under the New Revolving Credit Agreement are guaranteed by PCA's material subsidiaries. Loans under the New Revolving Credit Agreement bear interest at LIBOR plus an applicable margin. The applicable margin is determined based upon the public ratings of PCA's senior long-term unsecured debt or PCA's gross leverage ratio. The New Revolving Credit Agreement contains customary LIBOR successor rate provisions. The New Revolving Credit Agreement contains customary affirmative and negative covenants, including limitations on our ability to incur indebtedness at the subsidiary level and liens on our assets, and restrictions on our ability to engage in certain transactions involving mergers, consolidations, and sales of all or substantially all of our assets or the assets of a subsidiary guarantor. The New Revolving Credit Agreement has two financial covenants, a maximum leverage ratio and a minimum interest coverage ratio, each calculated on a consolidated basis. At September 30, 2021, we were in compliance with these covenants. PCA may prepay loans under the New Revolving Credit Agreement at any time without premium or penalty. Repayments, Interest, and Other For the nine months ended September 30, 2021 and 2020, cash payments for interest were $ 55.2 million and $ 56.9 million, respectively. Included in interest expense, net is the amortization of financing costs. For both the three months ended September 30, 2021 and 2020, amortization of financing costs was $ 0.5 million, and during both of the nine months ended September 30, 2021 and 2020, amortization of financing costs was $ 1.5 million. At September 30, 2021, we had $ 3,190.4 million of fixed-rate senior notes outstanding. The fair value of our fixed-rate debt was estimated to be $ 3,416.0 million. The difference between the book value and fair value is due to the difference between the period-end market interest rate and the stated rate of our fixed-rate debt. We estimated the fair value of our fixed-rate debt using quoted market prices (Level 2 inputs) within the fair value hierarchy, which is further defined in Note 2, Summary of Significant Accounting Policies, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2020 Annual Report on Form 10-K. For more information on our long-term debt and interest rates on that debt, see Note 10, Debt, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2020 Annual Report on Form 10-K.

Cash, Cash Equivalents, and Mar

Cash, Cash Equivalents, and Marketable Debt Securities	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash, Cash Equivalents, and Marketable Debt Securities	12. Cash, Cash Equivalents, and Marketable Debt Securities The following table shows the Company’s cash and available-for-sale (AFS) debt securities by major asset category at September 30, 2021 and December 31, 2020 (in millions): September 30, 2021 Adjusted Unrealized Unrealized Fair Cash and Short-Term Long-Term Cash and cash equivalents $ 1,695.4 $ — $ — $ 1,695.4 $ 1,695.4 $ — $ — Level 1 (a) : Money market funds 7.0 — — 7.0 7.0 — — U.S. Treasury securities 27.6 — — 27.6 — 19.3 8.3 Subtotal 34.6 — — 34.6 7.0 19.3 8.3 Level 2 (b) : Certificates of deposit 3.9 — — 3.9 — 3.9 — U.S. government agency securities 5.3 — — 5.3 — 4.0 1.3 Corporate debt securities 109.7 0.1 — 109.8 0.5 61.1 48.2 Subtotal 118.9 0.1 — 119.0 0.5 69.0 49.5 Total $ 1,848.9 $ 0.1 $ — $ 1,849.0 $ 1,702.9 $ 88.3 $ 57.8 December 31, 2020 Adjusted Unrealized Unrealized Fair Cash and Short-Term Long-Term Cash and cash equivalents $ 970.5 $ — $ — $ 970.5 $ 970.5 $ — $ — Level 1 (a) : Money market funds 0.6 — — 0.6 0.6 — — U.S. Treasury securities 28.1 0.2 — 28.3 — 18.9 9.4 Subtotal 28.7 0.2 — 28.9 0.6 18.9 9.4 Level 2 (b) : Certificates of deposit 5.9 — — 5.9 1.1 4.8 — Commercial paper 3.2 — — 3.2 1.0 2.2 — U.S. government agency securities 6.6 — — 6.6 — 2.6 4.0 Corporate debt securities 107.5 0.3 — 107.8 1.4 77.1 29.3 Subtotal 123.2 0.3 — 123.5 3.5 86.7 33.3 Total $ 1,122.4 $ 0.5 $ — $ 1,122.9 $ 974.6 $ 105.6 $ 42.7 (a) Valuations based on quoted prices for identical assets or liabilities in active markets. (b) Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. For the three and nine months ended September 30, 2021 and 2020, net realized gains and losses on the sales and maturities of certain marketable debt securities were insignificant. The Company invests in highly rated securities, with the primary objective of minimizing the potential risk of principal loss. The Company’s investment policy requires securities to be investment grade and limits the amount of credit exposure to any one issuer. The maturities of the Company’s long-term marketable debt securities generally range from one to two years . Fair values were determined for each individual marketable debt security in the investment portfolio. When evaluating a marketable debt security for impairment, PCA reviews factors such as the duration and extent to which the fair value of the marketable debt security is less than its cost, the financial condition of the issuer and any changes thereto, the general market condition in which the issuer operates, and PCA’s intent to sell, or whether it will be more likely than not be required to sell, the marketable debt security before recovery of its amortized cost basis. As of September 30, 2021 and December 31, 2020, we do no t consider any of the impairments related to our marketable debt securities to be the result of credit losses. Therefore, we have no t recorded an allowance for credit losses related to our marketable debt securities. All unrealized gains and losses were recorded in other comprehensive income (OCI). The following table provides information about the Company’s marketable debt securities that have been in a continuous loss position as of September 30, 2021 and December 31, 2020 (in millions, except number of marketable debt securities in a loss position): September 30, 2021 December 31, 2020 Fair Value of Number of Marketable Unrealized Fair Value of Number of Marketable Unrealized Corporate debt securities $ 50.0 63 $ — $ 42.9 56 $ — U.S. Treasury securities 8.1 10 — 1.7 3 — U.S. government agency securities 0.8 2 — — — — Certificates of deposit 0.5 1 — 1.3 2 — Commercial paper — — — 2.2 1 — $ 59.4 76 $ — $ 48.1 62 $ — (c) Unrealized losses were insignificant for the periods ended September 30, 2021 and December 31, 2020.

Employee Benefit Plans and Othe

Employee Benefit Plans and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Employee Benefit Plans and Other Postretirement Benefits	13. Employee Benefit Plans and Other Postretirement Benefits The components of net periodic benefit cost for our pension plans were as follows (dollars in millions): Pension Plans Three Months Ended Nine Months Ended 2021 2020 2021 2020 Service cost $ 5.4 $ 5.4 $ 16.0 $ 17.3 Interest cost 7.4 9.9 22.2 29.8 Expected return on plan assets ( 15.8 ) ( 14.2 ) ( 47.3 ) ( 42.6 ) Net amortization of unrecognized amounts Prior service cost 1.0 1.1 2.9 3.3 Actuarial loss 2.6 2.7 7.8 8.1 Net periodic benefit cost $ 0.6 $ 4.9 $ 1.6 $ 15.9 PCA makes pension plan contributions that are sufficient to fund its actuarially determined costs, generally equal to the minimum amounts required by the Employee Retirement Income Security Act (ERISA). From time to time, PCA may make additional discretionary contributions based on the funded status of the plans, tax deductibility, income from operations, and other factors. During the three and nine months ended September 30, 2021 and 2020, payments to our nonqualified pension plans were insignificant. During both the three and nine months ended September 30, 2021, we made contributions of $ 50.0 million to our qualified pension plans, and for the three and nine months ended September 30, 2020, we made contributions of $ 71.4 million and $ 82.5 million, respectively, to our qualified pension plans. We do not have a required minimum contribution amount established for 2021, but we expect to make discretionary contributions to our plans. For the three and nine months ended September 30, 2021 and 2020, the net periodic benefit cost for our postretirement plans was insignificant.

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement, Noncash Expense [Abstract]
Share-Based Compensation	14. Share-Based Compensation The Company has a long-term equity incentive plan, which allows for grants of restricted stock, performance awards, stock appreciation rights, and stock options to directors, officers, and employees, as well as others who engage in services for PCA. On February 25, 2020, our board of directors approved and, on May 5, 2020, our stockholders approved, the amendment and restatement of the plan. The amendment extended the plan’s term to May 5, 2030 and increased the number of shares of common stock available for issuance under the plan by 1.4 million shares. The total number of shares authorized for past and future awards is 12.0 million shares. As of September 30, 2021, assuming performance units are paid out at the target level of performance, 1.2 million shares were available for future grants under the current plan . Forfeitures are added back to the pool of shares of common stock available to be granted at a future date. The following table presents restricted stock and performance unit award activity for the nine months ended September 30, 2021: Restricted Stock Performance Units Shares Weighted Shares Weighted Outstanding at January 1, 2021 669,102 $ 102.55 357,417 $ 103.63 Granted 173,970 134.10 95,236 140.47 Vested (a) ( 164,483 ) 108.73 ( 74,894 ) 134.53 Forfeitures ( 6,692 ) 110.47 ( 19,667 ) 132.58 Outstanding at September 30, 2021 671,897 $ 109.13 358,092 $ 105.38 (a) Upon vesting of the performance unit awards, PCA issued 81,577 shares, which includes 6,683 shares for dividends accrued during the vesting period. Compensation Expense Our share-based compensation expense is recorded in "Selling, general, and administrative expenses." Compensation expense for share-based awards recognized in the Consolidated Statements of Income, net of forfeitures, was as follows (dollars in millions): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Restricted stock $ 3.9 $ 3.2 $ 18.4 $ 16.8 Performance units 2.9 2.8 8.5 7.0 Total share-based compensation expense 6.8 6.0 26.9 23.8 Income tax benefit ( 1.7 ) ( 1.5 ) ( 6.8 ) ( 6.0 ) Share-based compensation expense, net of tax benefit $ 5.1 $ 4.5 $ 20.1 $ 17.8 The fair value of restricted stock is determined based on the closing price of the Company’s stock on the grant date. Compensation expense, net of estimated forfeitures, is recorded over the requisite service period. As PCA’s Board of Directors has the ability to accelerate the vesting of these awards upon an employee’s retirement, the Company accelerates the recognition of compensation expense for certain employees approaching normal retirement age. Performance unit awards granted to certain key employees are earned based on the achievement of defined performance rankings of Return on Invested Capital (ROIC) or Total Shareholder Return (TSR) compared to ROIC and TSR for peer companies. For performance unit awards made in 2021 and 2020, in terms of grant date value, 50 % used TSR as the performance measure and 50 % used ROIC as the performance measure. The ROIC component of performance unit awards is valued based on the closing price of the stock on the grant date. As the ROIC component contains a performance condition, compensation expense, net of estimated forfeitures, is recorded over the requisite service period based on the most probable number of awards expected to vest. The TSR component of performance unit awards is valued using a Monte Carlo simulation as the TSR component contains a market condition. The Monte Carlo simulation estimates the fair value of the TSR component based on the expected term of the award, a risk-free interest rate, expected dividends, and expected volatility of the Company’s common stock and the common stock of the peer companies. Compensation expense is recorded ratably over the expected term of the award. The unrecognized compensation expense for all share-based awards at September 30, 2021 was as follows (dollars in millions): September 30, 2021 Unrecognized Remaining Restricted stock $ 30.6 2.6 Performance units 21.6 2.3 Total unrecognized share-based compensation expense $ 52.2 2.5

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	15. Stockholders' Equity Dividends During the nine months ended September 30, 2021, we paid $ 284.8 million of dividends to shareholders. On August 25, 2021, PCA’s Board of Directors declared a regular quarterly cash dividend of $ 1.00 per share of common stock, which was paid on October 15, 2021 to shareholders of record as of September 15, 2021. The dividend payment was $ 95.0 million. Repurchases of Common Stock On February 25, 2016, PCA announced that its Board of Directors authorized the repurchase of $ 200.0 million of the Company’s outstanding common stock. Repurchases may be made from time to time in open market or privately negotiated transactions in accordance with applicable securities regulations. The timing and amount of repurchases will be determined by the Company in its discretion based on factors such as PCA’s stock price and market and business conditions. The Company did no t repurchase any shares of its common stock under this authority during the three and nine months ended September 30, 2021. At September 30, 2021, $ 193.0 million of the authorized amount remained available for repurchase of the Company’s common stock. Accumulated Other Comprehensive Income (Loss) Changes in accumulated other comprehensive income (loss) (AOCI) by component were as follows (dollars in millions). Amounts in parentheses indicate losses: Foreign Unrealized Loss Unrealized Loss Unfunded Total Balance at January 1, 2021 $ ( 0.4 ) $ ( 0.2 ) $ 0.3 $ ( 144.2 ) $ ( 144.5 ) Other comprehensive income before reclassifications, — — ( 0.2 ) — ( 0.2 ) Amounts reclassified from AOCI, net of tax 0.4 — — 7.5 7.9 Balance at September 30, 2021 $ — $ ( 0.2 ) $ 0.1 $ ( 136.7 ) $ ( 136.8 ) Reclassifications out of AOCI were as follows (dollars in millions). Amounts in parentheses indicate expenses in the Consolidated Statements of Income: Amounts Reclassified from AOCI Three Months Ended September 30, Nine Months Ended September 30, Details about AOCI Components 2021 2020 2021 2020 Unfunded employee benefit obligations (a) Amortization of prior service costs $ ( 0.8 ) $ ( 1.0 ) $ ( 2.5 ) $ ( 3.0 ) See (a) below Amortization of actuarial losses ( 2.5 ) ( 2.6 ) ( 7.5 ) ( 7.8 ) See (a) below ( 3.3 ) ( 3.6 ) ( 10.0 ) ( 10.8 ) Total before tax 0.8 0.9 2.5 2.7 Tax benefit $ ( 2.5 ) $ ( 2.7 ) $ ( 7.5 ) $ ( 8.1 ) Net of tax (a) These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 13, Employee Benefit Plans and Other Postretirement Benefits, for additional information.

Concentrations of Risk

Concentrations of Risk	9 Months Ended
	Sep. 30, 2021
Risks and Uncertainties [Abstract]
Concentration of Risk	16. Concentrations of Risk Our Paper segment has a long-standing commercial and contractual relationship with Office Depot, our largest customer in the paper business. This relationship exposes us to a significant concentration of business and financial risk. Our sales to Office Depot represent approximately 4 % and 5 % of our total Company sales revenue for the nine month periods ended September 30, 2021 and 2020, respectively, and approximately 48 % and 43 % of our Paper segment sales revenue for both of those periods, respectively. For full year 2020, sales to Office Depot represented 45 % of our Paper segment sales. At September 30, 2021 and December 31, 2020, we had $ 47.7 million and $ 39.6 million of accounts receivable due from Office Depot, respectively, which represents approximately 4 % and 5 % of our total Company accounts receivable, respectively.

Transactions With Related Parti

Transactions With Related Parties	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Transactions With Related Parties	17. Transactions With Related Parties Louisiana Timber Procurement Company, L.L.C. (LTP) is a variable-interest entity that is 50 % owned by PCA and 50 % owned by Boise Cascade Company (Boise Cascade). LTP procures sawtimber, pulpwood, residual chips, and other residual wood fiber to meet the wood and fiber requirements of PCA and Boise Cascade in Louisiana. PCA is the primary beneficiary of LTP and has the power to direct the activities that most significantly affect the economic performance of LTP. Therefore, we consolidate 100% of LTP in our financial statements in our Corporate and Other segment. The carrying amounts of LTP's assets and liabilities (which relate primarily to non-inventory working capital items) on our Consolidated Balance Sheets were $ 2.5 million at both September 30, 2021 and December 31, 2020. During the three months ended September 30, 2021 and 2020, we recorded $ 22.3 million and $ 15.6 million, respectively, and during the nine months ended September 30, 2021 and 2020, we recorded $ 63.3 million and $ 52.0 million, respectively, of LTP sales to Boise Cascade in "Net Sales" in the Consolidated Statements of Income and approximately the same amount of expenses in "Cost of Sales". During the three months ended September 30, 2021 and 2020, fiber purchases from related parties were $ 3.6 million and $ 2.8 million , respectively. Fiber purchases from related parties were $ 10.3 million and $ 9.5 million for the nine months ended September 30, 2021 and 2020. Most of these purchases related to chip and log purchases by LTP from Boise Cascade's wood products business. These purchases are recorded in "Cost of Sales" in the Consolidated Statements of Income.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Segment Information	18. Segment Information We report our business in three reportable segments: Packaging, Paper, and Corporate and Other. These segments represent distinct businesses that are managed separately because of differing products and services. Each of these businesses requires distinct operating and marketing strategies. During the fourth quarter of 2020, in order to meet strong packaging demand and maintain appropriate inventory levels, we temporarily began producing linerboard on the No. 3 machine at our Jackson, Alabama mill. In the first quarter of 2021, we announced the discontinuation of production of uncoated freesheet paper grades on the machine and the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. Before October 2020, operating results for the Jackson mill were included in the Paper segment. Beginning in October 2020, operating results for the Jackson mill are included in both the Packaging and Paper segments. Each segment’s profits and losses are measured on operating profits before interest expense, net, non-operating pension income, and income taxes. For certain allocated expenses, the related assets and liabilities remain in the Corporate and Other segment. Selected financial information by reportable segment was as follows (dollars in millions): Sales, net Three Months Ended September 30, 2021 Trade Intersegment Total Operating Income (Loss) Packaging $ 1,825.0 $ 4.4 $ 1,829.4 $ 365.2 (a) Paper 150.3 — 150.3 11.0 (a) Corporate and Other 24.8 36.5 61.3 ( 23.4 ) (a) Intersegment eliminations — ( 40.9 ) ( 40.9 ) — $ 2,000.1 $ — $ 2,000.1 352.8 Non-operating pension income 5.0 Interest expense, net ( 23.9 ) (a) Income before taxes $ 333.9 Sales, net Three Months Ended September 30, 2020 Trade Intersegment Total Operating Income (Loss) Packaging $ 1,497.6 $ 3.5 $ 1,501.1 $ 222.4 (b) Paper 178.1 — 178.1 7.3 Corporate and Other 18.0 30.8 48.8 ( 20.2 ) Intersegment eliminations — ( 34.3 ) ( 34.3 ) — $ 1,693.7 $ — $ 1,693.7 209.5 Non-operating pension income 0.6 Interest expense, net ( 24.4 ) Income before taxes $ 185.7 Sales, net Nine Months Ended September 30, 2021 Trade Intersegment Total Operating Income (Loss) Packaging $ 5,159.3 $ 12.1 $ 5,171.4 $ 940.3 (a) Paper 457.0 0.1 457.1 22.3 (a) Corporate and Other 70.8 101.0 171.8 ( 76.9 ) (a) Intersegment eliminations — ( 113.2 ) ( 113.2 ) — $ 5,687.1 $ — $ 5,687.1 885.7 Non-operating pension income 14.8 Interest expense, net ( 72.2 ) (a) Income before taxes $ 828.3 Sales, net Nine Months Ended September 30, 2020 Trade Intersegment Total Operating Income (Loss) Packaging $ 4,364.8 $ 13.7 $ 4,378.5 $ 619.9 (b)(c) Paper 518.7 — 518.7 ( 21.7 ) (c)(d) Corporate and Other 60.5 99.2 159.7 ( 63.5 ) Intersegment eliminations — ( 112.9 ) ( 112.9 ) — $ 4,944.0 $ — $ 4,944.0 534.7 Non-operating pension income 1.7 Interest expense, net ( 69.1 ) Income before taxes $ 467.3 (a) The three and nine months ended September 30, 2021 include the following: 1. $ 4.5 million and $ 9.4 million, respectively, of charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. 2. $ 2.7 million and $ 0.1 million, respectively, of charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities. 3. $ 0.5 million of costs related to the Company's September 2021 debt refinancing, which included the issuance of the new 3.05 % Senior Notes due 2051. (b) The three and nine months ended September 30, 2020 include the following: 1. $ 3.3 million and $ 24.1 million of charges, respectively, consisting of closure costs related to corrugated products facilities, substantially all of which relates to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020. 2. $ 10.0 million of charges related to the impact of Hurricane Laura at our DeRidder, Louisiana mill, including unabsorbed costs related to lost production, excess purchased containerboard and freight costs, repair expenses, rental and supplies costs, and other recovery expenses. (c) The nine months ended September 20, 2020 include $ 6.9 million of incremental, out-of-pocket costs related to COVID-19, including supplies, cleaning and sick pay. Beginning in July 2020, all corresponding COVID-19 related expenses were included in normalized costs. (d) 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.

Commitments, Guarantees, Indemn

Commitments, Guarantees, Indemnifications and Legal Proceedings	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments, Guarantees, Indemnifications and Legal Proceedings	19. Commitments, Guarantees, Indemnifications and Legal Proceedings We have financial commitments and obligations that arise in the ordinary course of our business. These include long-term debt, capital commitments, lease obligations, and purchase commitments for goods and services, and legal proceedings, all of which are discussed in Note 10, Debt, and Note 20, Commitments, Guarantees, Indemnifications, and Legal Proceedings, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2020 Annual Report on Form 10-K. Guarantees and Indemnifications We provide guarantees, indemnifications, and other assurances to third parties in the normal course of our business. These include tort indemnifications, product guarantees, environmental assurances, and representations and warranties in commercial agreements. At September 30, 2021, we are not aware of any material liabilities arising from any guarantee, indemnification, or financial assurance we have provided. If we determined such a liability was probable and subject to reasonable determination, we would accrue for it at that time. DeRidder Mill Incident On February 8, 2017 , a tank located in the pulp mill at the Company's DeRidder, Louisiana facility exploded, resulting in three contractor fatalities and other injuries. The Company has been served with multiple lawsuits involving the decedents and other allegedly injured parties, alleging negligence on the part of the Company and claiming compensatory and punitive damages. The Company is vigorously defending these lawsuits. The Company believes that these suits are covered by its liability insurance policies, subject to an aggregate $ 1.0 million deductible, which has been satisfied in full as a result of settlement of various lawsuits and fees and expenses incurred by the Company. Cases involving nine plaintiffs are pending in the U.S. District Court for the Middle District of Louisiana and one case remains pending in state court in Alabama. One case previously dismissed by the federal district court for the Western District of Louisiana has been appealed by the plaintiff to the United States Court of Appeals for the Fifth Circuit. The remaining lawsuits pending in federal district court and state court are in the early stages. Accordingly, the Company is unable to estimate a range of reasonable possible losses at this time. The Company has cooperated with investigations from the U.S. Occupational Health and Safety Administration (OSHA), the U.S. Chemical Safety Board (CSB) and the U.S. Environmental Protection Agency (EPA). The U.S. Chemical Safety Board completed its investigation and issued its report during the second quarter of 2018. The Company settled with OSHA during the second quarter of 2018 and paid approximately $ 40,000 in penalties for citations. The EPA investigation is ongoing. In May 2017, the EPA conducted an on-site inspection of the facility to assess compliance with the Clean Air Act, Risk Management Program (RMP). The Company provided additional information to the EPA promptly after the inspection to address certain areas of concern (AOCs) observed during the inspection. In January 2021, the EPA and U.S. Department of Justice (DOJ) initiated civil judicial enforcement discussions with PCA. These discussions are ongoing. As of the date of filing of this report, no complaint has been filed. PCA continues to cooperate with the agencies. Since the inspection in 2017, PCA performed several voluntary activities to address the AOCs presented in the EPA’s inspection report and has removed the RMP covered process from the facility. Environmental Matters On August 8, 2019, the EPA issued a notice of violation (NOV) alleging violations of the Clean Air Act, resulting from an inspection of our Wallula, Washington mill in September 2018. PCA denies the violations set forth in the NOV and has requested that the EPA’s Office of Air Quality Planning and Standards provide an applicability determination to clarify that the relevant operations of PCA have not violated the regulations at issue in the NOV. The EPA denied our request in 2020. We intend to vigorously defend any enforcement action and, on July 27, 2020, filed a petition with the EPA to reconsider its denial of our applicability determination and filed petitions in U.S. federal court to review the agency’s denial of our applicability determination as well as the rule at issue. While we cannot predict with certainty the ultimate resolution of this matter, we believe that we have a meritorious position that our operations have not violated the Clean Air Act, that we have taken appropriate action to address the matters raised by the EPA in the NOV, and that this matter will not result in a material adverse effect on our financial condition, results of operations, or cash flows. Legal Proceedings We are also a party to various legal actions arising in the ordinary course of our business. These legal actions include commercial liability claims, premises liability claims, and employment-related claims, among others. As of the date of this filing, we believe it is not reasonably possible that any of the legal actions against us will, either individually or in the aggregate, have a material adverse effect on our financial condition, results of operations, or cash flows.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	20. Subsequent Events The Company has disclosed the following subsequent events in accordance with Accounting Standards Codification (ASC) 855, Subsequent Events . Subsequent events have been evaluated through the filing date of this Form 10-Q. On October 22, 2021, we entered into a definitive agreement to acquire substantially all of the assets of Advance Packaging Corporation, an independent corrugated products producer, in a cash-free, debt-free transaction, for a cash purchase price of $ 189 million. Advance Packaging is a full-service producer of corrugated packaging products, including graphics, retail displays, sustainable shipping containers, and protective packaging. Advance Packaging owns and operates a 500,000 square foot corrugated products facility in Grand Rapids, Michigan. Closing is subject to certain customary conditions and is expected in the fourth quarter of 2021. PCA expects to finance the transaction with cash-on-hand. The operating results of Advance Packaging will be included in PCA's results upon closing of the transaction.

Nature of Operations and Basi_2

Nature of Operations and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting and Presentation	The consolidated financial statements of PCA as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 are unaudited but include all adjustments (consisting only of normal recurring adjustments) that management considers necessary for a fair presentation of such financial statements. The preparation of the consolidated financial statements involves the use of estimates and accruals. Actual results may vary from those estimates. These financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and notes required by accounting principles generally accepted in the United States for complete audited financial statements. Operating results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. These consolidated financial statements should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2020.
Use of Estimates	The preparation of the consolidated financial statements involves the use of estimates and accruals. Actual results may vary from those estimates.
Revenue Recognition	Revenue Recognition Revenue is recognized when control of the promised goods or services is transferred to customers in an amount that reflects the consideration expected to be received in exchange for those goods or services. Sales, value added, and other taxes collected concurrently with revenue-producing activities are excluded from revenue. The following table presents our revenues disaggregated by product line (dollars in millions): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Packaging $ 1,829.4 $ 1,501.1 $ 5,171.4 $ 4,378.5 Paper 150.3 178.1 457.1 518.7 Corporate and Other 20.4 14.5 58.6 46.8 Total revenue $ 2,000.1 $ 1,693.7 $ 5,687.1 $ 4,944.0
Inventory Valuation	We value our raw materials, work in process, and finished goods inventories using lower of cost, as determined by the average cost method, or net realizable value. Supplies and materials are valued at the first-in, first-out (FIFO) or average cost methods.

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Summary of Revenues Disaggregated by Product Line	The following table presents our revenues disaggregated by product line (dollars in millions): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Packaging $ 1,829.4 $ 1,501.1 $ 5,171.4 $ 4,378.5 Paper 150.3 178.1 457.1 518.7 Corporate and Other 20.4 14.5 58.6 46.8 Total revenue $ 2,000.1 $ 1,693.7 $ 5,687.1 $ 4,944.0

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Computation of Basic and Diluted Income Per Common Share	The following table sets forth the computation of basic and diluted income per common share for the periods presented (dollars and shares in millions, except per share data): Three Months Ended Nine Months Ended September 30, September 30, Numerator: 2021 2020 2021 2020 Net income $ 250.7 $ 139.1 $ 624.6 $ 337.4 Less: Distributed and undistributed earnings allocated to participating ( 1.7 ) ( 1.0 ) ( 4.9 ) ( 2.7 ) Net income attributable to common shareholders $ 249.0 $ 138.1 $ 619.7 $ 334.7 Denominator: Weighted average basic common shares outstanding 94.3 94.2 94.2 94.0 Effect of dilutive securities 0.4 0.3 0.4 0.4 Weighted average diluted common shares outstanding 94.7 94.5 94.6 94.4 Basic income per common share $ 2.64 $ 1.47 $ 6.58 $ 3.56 Diluted income per common share $ 2.63 $ 1.46 $ 6.55 $ 3.54

Other Expense, Net (Tables)

Other Expense, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Other Income and Expenses [Abstract]
Components of Other Income (Expense), Net	The components of other income (expense), net, were as follows (dollars in millions): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Asset disposals and write-offs $ ( 6.4 ) $ ( 5.5 ) $ ( 27.3 ) $ ( 16.5 ) Jackson mill conversion-related activities (a) ( 3.2 ) — ( 6.1 ) — Facilities closure and other income (costs) (b) ( 0.7 ) ( 2.9 ) 2.7 ( 16.6 ) Other ( 3.1 ) ( 0.4 ) ( 11.0 ) ( 3.8 ) Total $ ( 13.4 ) $ ( 8.8 ) $ ( 41.7 ) $ ( 36.9 ) (a) Includes charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. (b) For the three months ended September 30, 2021, includes charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities, partially offset by closure costs related to corrugated products facilities. For 2020, includes costs primarily related to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020.

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Components of Inventories	The components of inventories were as follows (dollars in millions): September 30, December 31, 2021 2020 Raw materials $ 323.3 $ 263.5 Work in process 16.1 11.6 Finished goods 190.6 183.6 Supplies and materials 350.1 329.2 Inventories $ 880.1 $ 787.9

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Components of Property, Plant, and Equipment	The components of property, plant, and equipment were as follows (dollars in millions): September 30, December 31, 2021 2020 Land and land improvements $ 186.2 $ 179.6 Buildings 895.5 858.5 Machinery and equipment 6,055.2 5,826.6 Construction in progress 417.5 360.0 Other 97.4 88.8 Property, plant and equipment, at cost 7,651.8 7,313.5 Less accumulated depreciation ( 4,291.0 ) ( 4,120.1 ) Property, plant, and equipment, net $ 3,360.8 $ 3,193.4

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Components of Intangible Assets	The weighted average remaining useful life, gross carrying amount, and accumulated amortization of our intangible assets were as follows (dollars in millions): September 30, 2021 December 31, 2020 Weighted Gross Accumulated Weighted Gross Accumulated Customer relationships 8.4 $ 503.8 $ 246.2 9.1 $ 503.8 $ 220.2 Trademarks and trade names 9.3 34.8 24.8 9.3 34.8 23.0 Other 0.9 4.3 4.2 1.2 4.3 3.8 Total intangible assets (excluding goodwill) 8.5 $ 542.9 $ 275.2 9.1 $ 542.9 $ 247.0

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities [Abstract]
Components of Accrued Liabilities	The components of accrued liabilities were as follows (dollars in millions): September 30, December 31, 2021 2020 Compensation and benefits $ 144.5 $ 126.5 Customer rebates and other credits 36.3 27.1 Medical insurance and workers’ compensation 26.5 25.5 Property, franchise, sales and use taxes 26.3 16.5 Environmental liabilities and asset retirement obligations 3.8 4.6 Severance, retention, and relocation 2.1 4.1 Other 13.0 11.9 Total $ 252.5 $ 216.2

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Summary of Debt	At September 30, 2021 and December 31, 2020, our long-term debt and interest rates on that debt were as follows (dollars in millions): September 30, December 31, 2021 2020 Revolving Credit Facility, due August 2021, terminated June 2021 $ — $ — Revolving Credit Facility, due June 2026 — — 4.50 % Senior Notes, net of discount of $ 0.5 million and 0.6 million as of September 30, 2021 and December 31, 2020, 699.5 699.4 3.65 % Senior Notes, net of discount of $ 0.4 million and 0.5 million as of September 30, 2021 and December 31, 2020, 399.6 399.5 3.40 % Senior Notes, net of discount of $ 1.1 million and 1.2 million as of September 30, 2021 and December 31, 2020, 498.9 498.8 3.00 % Senior Notes, net of discount of $ 0.5 million and 0.6 million as of September 30, 2021 and December 31, 2020, 499.5 499.4 4.05 % Senior Notes, net of discount of $ 3.4 million as of both 396.6 396.6 3.05 % Senior Notes, net of discount of $ 3.7 million as of October 2051 696.3 — Total 3,190.4 2,493.7 Less current portion (a) 698.1 — Less unamortized debt issuance costs 21.2 14.3 Total long-term debt $ 2,471.1 $ 2,479.4 (a) The current portion of long-term debt excludes unamortized debt issuance costs of $ 1.4 million at September 30, 2021.

Cash, Cash Equivalents, and M_2

Cash, Cash Equivalents, and Marketable Debt Securities (Tables)	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Schedule of Cash and Available-For-Sale Debt Securities by Major Asset Category	The following table shows the Company’s cash and available-for-sale (AFS) debt securities by major asset category at September 30, 2021 and December 31, 2020 (in millions): September 30, 2021 Adjusted Unrealized Unrealized Fair Cash and Short-Term Long-Term Cash and cash equivalents $ 1,695.4 $ — $ — $ 1,695.4 $ 1,695.4 $ — $ — Level 1 (a) : Money market funds 7.0 — — 7.0 7.0 — — U.S. Treasury securities 27.6 — — 27.6 — 19.3 8.3 Subtotal 34.6 — — 34.6 7.0 19.3 8.3 Level 2 (b) : Certificates of deposit 3.9 — — 3.9 — 3.9 — U.S. government agency securities 5.3 — — 5.3 — 4.0 1.3 Corporate debt securities 109.7 0.1 — 109.8 0.5 61.1 48.2 Subtotal 118.9 0.1 — 119.0 0.5 69.0 49.5 Total $ 1,848.9 $ 0.1 $ — $ 1,849.0 $ 1,702.9 $ 88.3 $ 57.8 December 31, 2020 Adjusted Unrealized Unrealized Fair Cash and Short-Term Long-Term Cash and cash equivalents $ 970.5 $ — $ — $ 970.5 $ 970.5 $ — $ — Level 1 (a) : Money market funds 0.6 — — 0.6 0.6 — — U.S. Treasury securities 28.1 0.2 — 28.3 — 18.9 9.4 Subtotal 28.7 0.2 — 28.9 0.6 18.9 9.4 Level 2 (b) : Certificates of deposit 5.9 — — 5.9 1.1 4.8 — Commercial paper 3.2 — — 3.2 1.0 2.2 — U.S. government agency securities 6.6 — — 6.6 — 2.6 4.0 Corporate debt securities 107.5 0.3 — 107.8 1.4 77.1 29.3 Subtotal 123.2 0.3 — 123.5 3.5 86.7 33.3 Total $ 1,122.4 $ 0.5 $ — $ 1,122.9 $ 974.6 $ 105.6 $ 42.7 (a) Valuations based on quoted prices for identical assets or liabilities in active markets. (b) Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.
Schedule of Marketable Debt Securities in Continuous Loss Position	The following table provides information about the Company’s marketable debt securities that have been in a continuous loss position as of September 30, 2021 and December 31, 2020 (in millions, except number of marketable debt securities in a loss position): September 30, 2021 December 31, 2020 Fair Value of Number of Marketable Unrealized Fair Value of Number of Marketable Unrealized Corporate debt securities $ 50.0 63 $ — $ 42.9 56 $ — U.S. Treasury securities 8.1 10 — 1.7 3 — U.S. government agency securities 0.8 2 — — — — Certificates of deposit 0.5 1 — 1.3 2 — Commercial paper — — — 2.2 1 — $ 59.4 76 $ — $ 48.1 62 $ — (c) Unrealized losses were insignificant for the periods ended September 30, 2021 and December 31, 2020.

Employee Benefit Plans and Ot_2

Employee Benefit Plans and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Costs	The components of net periodic benefit cost for our pension plans were as follows (dollars in millions): Pension Plans Three Months Ended Nine Months Ended 2021 2020 2021 2020 Service cost $ 5.4 $ 5.4 $ 16.0 $ 17.3 Interest cost 7.4 9.9 22.2 29.8 Expected return on plan assets ( 15.8 ) ( 14.2 ) ( 47.3 ) ( 42.6 ) Net amortization of unrecognized amounts Prior service cost 1.0 1.1 2.9 3.3 Actuarial loss 2.6 2.7 7.8 8.1 Net periodic benefit cost $ 0.6 $ 4.9 $ 1.6 $ 15.9

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement, Noncash Expense [Abstract]
Summary of Restricted Stock and Performance Unit Award Activity	The following table presents restricted stock and performance unit award activity for the nine months ended September 30, 2021: Restricted Stock Performance Units Shares Weighted Shares Weighted Outstanding at January 1, 2021 669,102 $ 102.55 357,417 $ 103.63 Granted 173,970 134.10 95,236 140.47 Vested (a) ( 164,483 ) 108.73 ( 74,894 ) 134.53 Forfeitures ( 6,692 ) 110.47 ( 19,667 ) 132.58 Outstanding at September 30, 2021 671,897 $ 109.13 358,092 $ 105.38 (a) Upon vesting of the performance unit awards, PCA issued 81,577 shares, which includes 6,683 shares for dividends accrued during the vesting period.
Compensation Expense for Share-Based Awards	Our share-based compensation expense is recorded in "Selling, general, and administrative expenses." Compensation expense for share-based awards recognized in the Consolidated Statements of Income, net of forfeitures, was as follows (dollars in millions): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Restricted stock $ 3.9 $ 3.2 $ 18.4 $ 16.8 Performance units 2.9 2.8 8.5 7.0 Total share-based compensation expense 6.8 6.0 26.9 23.8 Income tax benefit ( 1.7 ) ( 1.5 ) ( 6.8 ) ( 6.0 ) Share-based compensation expense, net of tax benefit $ 5.1 $ 4.5 $ 20.1 $ 17.8
Unrecognized Compensation Expense for Share-Based Awards	The unrecognized compensation expense for all share-based awards at September 30, 2021 was as follows (dollars in millions): September 30, 2021 Unrecognized Remaining Restricted stock $ 30.6 2.6 Performance units 21.6 2.3 Total unrecognized share-based compensation expense $ 52.2 2.5

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Components of Changes in Accumulated Other Comprehensive Income (AOCI)	Changes in accumulated other comprehensive income (loss) (AOCI) by component were as follows (dollars in millions). Amounts in parentheses indicate losses: Foreign Unrealized Loss Unrealized Loss Unfunded Total Balance at January 1, 2021 $ ( 0.4 ) $ ( 0.2 ) $ 0.3 $ ( 144.2 ) $ ( 144.5 ) Other comprehensive income before reclassifications, — — ( 0.2 ) — ( 0.2 ) Amounts reclassified from AOCI, net of tax 0.4 — — 7.5 7.9 Balance at September 30, 2021 $ — $ ( 0.2 ) $ 0.1 $ ( 136.7 ) $ ( 136.8 )
Reclassifications Out of Accumulated Other Comprehensive Income (AOCI)	Reclassifications out of AOCI were as follows (dollars in millions). Amounts in parentheses indicate expenses in the Consolidated Statements of Income: Amounts Reclassified from AOCI Three Months Ended September 30, Nine Months Ended September 30, Details about AOCI Components 2021 2020 2021 2020 Unfunded employee benefit obligations (a) Amortization of prior service costs $ ( 0.8 ) $ ( 1.0 ) $ ( 2.5 ) $ ( 3.0 ) See (a) below Amortization of actuarial losses ( 2.5 ) ( 2.6 ) ( 7.5 ) ( 7.8 ) See (a) below ( 3.3 ) ( 3.6 ) ( 10.0 ) ( 10.8 ) Total before tax 0.8 0.9 2.5 2.7 Tax benefit $ ( 2.5 ) $ ( 2.7 ) $ ( 7.5 ) $ ( 8.1 ) Net of tax (a) These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 13, Employee Benefit Plans and Other Postretirement Benefits, for additional information.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Selected Financial Information by Reportable Segment	Selected financial information by reportable segment was as follows (dollars in millions): Sales, net Three Months Ended September 30, 2021 Trade Intersegment Total Operating Income (Loss) Packaging $ 1,825.0 $ 4.4 $ 1,829.4 $ 365.2 (a) Paper 150.3 — 150.3 11.0 (a) Corporate and Other 24.8 36.5 61.3 ( 23.4 ) (a) Intersegment eliminations — ( 40.9 ) ( 40.9 ) — $ 2,000.1 $ — $ 2,000.1 352.8 Non-operating pension income 5.0 Interest expense, net ( 23.9 ) (a) Income before taxes $ 333.9 Sales, net Three Months Ended September 30, 2020 Trade Intersegment Total Operating Income (Loss) Packaging $ 1,497.6 $ 3.5 $ 1,501.1 $ 222.4 (b) Paper 178.1 — 178.1 7.3 Corporate and Other 18.0 30.8 48.8 ( 20.2 ) Intersegment eliminations — ( 34.3 ) ( 34.3 ) — $ 1,693.7 $ — $ 1,693.7 209.5 Non-operating pension income 0.6 Interest expense, net ( 24.4 ) Income before taxes $ 185.7 Sales, net Nine Months Ended September 30, 2021 Trade Intersegment Total Operating Income (Loss) Packaging $ 5,159.3 $ 12.1 $ 5,171.4 $ 940.3 (a) Paper 457.0 0.1 457.1 22.3 (a) Corporate and Other 70.8 101.0 171.8 ( 76.9 ) (a) Intersegment eliminations — ( 113.2 ) ( 113.2 ) — $ 5,687.1 $ — $ 5,687.1 885.7 Non-operating pension income 14.8 Interest expense, net ( 72.2 ) (a) Income before taxes $ 828.3 Sales, net Nine Months Ended September 30, 2020 Trade Intersegment Total Operating Income (Loss) Packaging $ 4,364.8 $ 13.7 $ 4,378.5 $ 619.9 (b)(c) Paper 518.7 — 518.7 ( 21.7 ) (c)(d) Corporate and Other 60.5 99.2 159.7 ( 63.5 ) Intersegment eliminations — ( 112.9 ) ( 112.9 ) — $ 4,944.0 $ — $ 4,944.0 534.7 Non-operating pension income 1.7 Interest expense, net ( 69.1 ) Income before taxes $ 467.3 (a) The three and nine months ended September 30, 2021 include the following: 1. $ 4.5 million and $ 9.4 million, respectively, of charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities. 2. $ 2.7 million and $ 0.1 million, respectively, of charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities. 3. $ 0.5 million of costs related to the Company's September 2021 debt refinancing, which included the issuance of the new 3.05 % Senior Notes due 2051. (b) The three and nine months ended September 30, 2020 include the following: 1. $ 3.3 million and $ 24.1 million of charges, respectively, consisting of closure costs related to corrugated products facilities, substantially all of which relates to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020. 2. $ 10.0 million of charges related to the impact of Hurricane Laura at our DeRidder, Louisiana mill, including unabsorbed costs related to lost production, excess purchased containerboard and freight costs, repair expenses, rental and supplies costs, and other recovery expenses. (c) The nine months ended September 20, 2020 include $ 6.9 million of incremental, out-of-pocket costs related to COVID-19, including supplies, cleaning and sick pay. Beginning in July 2020, all corresponding COVID-19 related expenses were included in normalized costs. (d) 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.

Nature of Operations and Basi_3

Nature of Operations and Basis of Presentation - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Date of incorporation	Jan. 25, 1999
Number of reportable segments	3

Revenue - Summary of Revenues D

Revenue - Summary of Revenues Disaggregated by Product Line (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenue	$ 2,000.1	$ 1,693.7	$ 5,687.1	$ 4,944
Packaging
Disaggregation Of Revenue [Line Items]
Revenue	1,829.4	1,501.1	5,171.4	4,378.5
Paper
Disaggregation Of Revenue [Line Items]
Revenue	150.3	178.1	457.1	518.7
Corporate and Other
Disaggregation Of Revenue [Line Items]
Revenue	$ 20.4	$ 14.5	$ 58.6	$ 46.8

Revenue - Additional Informatio

Revenue - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021
Packaging Corporation of America
Revenue [Line Items]
Variable interest entity, ownership percentage	50.00%
Boise Cascade Co-Owner of LTP
Revenue [Line Items]
Variable interest entity, ownership percentage	50.00%

Earnings Per Share - Computatio

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income	$ 250.7	$ 139.1	$ 624.6	$ 337.4
Less: Distributed and undistributed earnings allocated to participating securities	(1.7)	(1)	(4.9)	(2.7)
Net income attributable to common shareholders	$ 249	$ 138.1	$ 619.7	$ 334.7
Denominator:
Weighted average basic common shares outstanding (in shares)	94.3	94.2	94.2	94
Effect of dilutive securities (in shares)	0.4	0.3	0.4	0.4
Weighted average diluted common shares outstanding (in shares)	94.7	94.5	94.6	94.4
Basic income per common share (in dollars per share)	$ 2.64	$ 1.47	$ 6.58	$ 3.56
Diluted income per common share (in dollars per share)	$ 2.63	$ 1.46	$ 6.55	$ 3.54

Other Expense, Net - Components

Other Expense, Net - Components of Other Income (Expense), Net (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset disposals and write-offs		$ (6.4)	$ (5.5)	$ (27.3)	$ (16.5)
Facilities closure and other income (costs)	[1]	(0.7)	(2.9)	2.7	(16.6)
Other		(3.1)	(0.4)	(11)	(3.8)
Total		(13.4)	(8.8)	(41.7)	(36.9)
Jackson, Alabama Mill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Conversion-related activities	[2]	$ (3.2)	$ 0	$ (6.1)	$ 0
[1]	For the three months ended September 30, 2021, includes charges consisting of closure costs related to corrugated products facilities. For the nine months ended September 30, 2021, these costs are partially offset by income primarily consisting of an adjustment of the required asset retirement obligation related to the 2020 closure of the San Lorenzo, California facility, a gain on sale of transportation assets, and insurance proceeds received for a natural disaster at one of the corrugated products facilities, partially offset by closure costs related to corrugated products facilities. For 2020, includes costs primarily related to the closure of the San Lorenzo, California facility during the second quarter of 2020, partially offset by income related to the sale of a corrugated products facility during the second quarter of 2020.
[2]	Includes charges related to the announced discontinuation of production of uncoated freesheet paper grades on the No. 3 machine at the Jackson, Alabama mill in the first quarter of 2021 associated with the permanent conversion of the machine to produce linerboard and other paper-to-containerboard conversion related activities.

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income tax provision	$ 83.2	$ 46.6	$ 203.7	$ 129.9
Effective income tax rate, percent	24.90%	5.00%	4.60%	27.80%
Corresponding charge			$ 0
Federal statutory income tax rate			21.00%
Cash paid for taxes, net of refunds received			$ 168.1	$ 65

Inventories - Components of Inv

Inventories - Components of Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 323.3	$ 263.5
Work in process	16.1	11.6
Finished goods	190.6	183.6
Supplies and materials	350.1	329.2
Inventories	$ 880.1	$ 787.9

Property, Plant, and Equipmen_2

Property, Plant, and Equipment - Components of Property, Plant, and Equipment (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	$ 7,651.8	$ 7,313.5
Less accumulated depreciation	(4,291)	(4,120.1)
Property, plant, and equipment, net	3,360.8	3,193.4
Land and Land Improvements
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	186.2	179.6
Buildings
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	895.5	858.5
Machinery and Equipment
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	6,055.2	5,826.6
Construction in Progress
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	417.5	360
Other
Property, Plant, And Equipment [Line Items]
Property, plant and equipment, at cost	$ 97.4	$ 88.8

Property, Plant, and Equipmen_3

Property, Plant, and Equipment - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	May 31, 2020
Depreciation [Abstract]
Depreciation expense	$ 95.5	$ 89.6	$ 279.9	$ 272.7
Incremental depreciation			3.6	$ 2.9
Purchases of property, plant, and equipment included in accounts payable			$ 112.1		$ 22.2
Paper
Property, Plant, And Equipment [Line Items]
Recoverability test results recoverable percentage						100.00%

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets -Goodwill - Additional Information (Details) - USD ($) $ in Millions	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill [Line Items]
Goodwill impairment charge		$ 0	$ 0			$ 0	$ 55.2
Discount rate utilized	0.09
Alternative Investment, Valuation Technique [Extensible List]	us-gaap:IncomeApproachValuationTechniqueMember
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember
Goodwill		863.5				863.5		$ 863.5
Packaging
Goodwill [Line Items]
Goodwill		$ 863.5				$ 863.5		$ 863.5
Paper
Goodwill [Line Items]
Recoverability test results recoverable percentage	100.00%
Paper Reporting Unit
Goodwill [Line Items]
Goodwill impairment charge	$ 55.2			$ 55.2	$ 55.2

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Components of Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (in Years)	8 years 6 months	9 years 1 month 6 days
Gross Carrying Amount	$ 542.9	$ 542.9
Accumulated Amortization	$ 275.2	$ 247
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (in Years)	8 years 4 months 24 days	9 years 1 month 6 days
Gross Carrying Amount	$ 503.8	$ 503.8
Accumulated Amortization	$ 246.2	$ 220.2
Trademarks and Trade Names
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (in Years)	9 years 3 months 18 days	9 years 3 months 18 days
Gross Carrying Amount	$ 34.8	$ 34.8
Accumulated Amortization	$ 24.8	$ 23
Other Intangible Assets
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (in Years)	10 months 24 days	1 year 2 months 12 days
Gross Carrying Amount	$ 4.3	$ 4.3
Accumulated Amortization	$ 4.2	$ 3.8

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets amortization expense	$ 28.2	$ 33.4
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Adjustment to decrease the remaining book value of intangible asset		$ 4.5

Accrued Liabilities - Component

Accrued Liabilities - Components of Accrued Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities, Current [Abstract]
Compensation and benefits	$ 144.5	$ 126.5
Customer rebates and other credits	36.3	27.1
Medical insurance and workers’ compensation	26.5	25.5
Property, franchise sales and use taxes	26.3	16.5
Environmental liabilities and asset retirement obligations	3.8	4.6
Severance, retention, and relocation	2.1	4.1
Other	13	11.9
Total	$ 252.5	$ 216.2

Debt - Summary of Debt (Details

Debt - Summary of Debt (Details) - USD ($) $ in Millions		Sep. 30, 2021	Sep. 21, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long term debt		$ 3,190.4		$ 2,493.7
Less current portion	[1]	698.1		0
Less unamortized debt issuance costs		21.2		14.3
Total Long term debt		2,471.1		2,479.4
Revolving Credit Facility, due August 2021 | Line Of Credit
Debt Instrument [Line Items]
Long term debt		0		0
Revolving Credit Facility, due June 2026 | Line Of Credit
Debt Instrument [Line Items]
Long term debt		0		0
4.50% Senior Notes, due November 2023 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 699.5		$ 699.4
Stated interest rate		4.50%		4.50%
3.65% Senior Notes, due September 2024 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 399.6		$ 399.5
Stated interest rate		3.65%		3.65%
3.40% Senior Notes, due December 2027 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 498.9		$ 498.8
Stated interest rate		3.40%		3.40%
3.00% Senior Notes, due December 2029 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 499.5		$ 499.4
Stated interest rate		3.00%		3.00%
4.05% Senior Notes, due December 2049 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 396.6		$ 396.6
Stated interest rate		4.05%		4.05%
3.05% Senior Notes, due October 2051 | Senior Notes
Debt Instrument [Line Items]
Long term debt		$ 696.3		$ 0
Stated interest rate		3.05%	3.05%
[1]	The current portion of long-term debt excludes unamortized debt issuance costs of $ 1.4 million at September 30, 2021.

Debt - Summary of Debt (Parenth

Debt - Summary of Debt (Parenthetical) (Details) - USD ($) $ in Millions	Sep. 21, 2021	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ 1.4
Revolving Credit Facility, due August 2021 | Line Of Credit
Debt Instrument [Line Items]
Credit facility, expiration date		Jun. 30, 2021	Jun. 30, 2021
Debt instrument, maturity date		Aug. 21, 2021	Aug. 21, 2021
Revolving Credit Facility, due June 2026 | Line Of Credit
Debt Instrument [Line Items]
Credit facility, expiration date		Jun. 30, 2026	Jun. 30, 2026
4.50% Senior Notes, due November 2023 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate		4.50%	4.50%
Senior notes, discount		$ 0.5	$ 0.6
Debt instrument, maturity date		Nov. 1, 2023	Nov. 1, 2023
3.65% Senior Notes, due September 2024 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate		3.65%	3.65%
Senior notes, discount		$ 0.4	$ 0.5
Debt instrument, maturity date		Sep. 15, 2024	Sep. 15, 2024
3.40% Senior Notes, due December 2027 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate		3.40%	3.40%
Senior notes, discount		$ 1.1	$ 1.2
Debt instrument, maturity date		Dec. 15, 2027	Dec. 15, 2027
3.00% Senior Notes, due December 2029 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate		3.00%	3.00%
Senior notes, discount		$ 0.5	$ 0.6
Debt instrument, maturity date		Dec. 15, 2029	Dec. 15, 2029
4.05% Senior Notes, due December 2049 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate		4.05%	4.05%
Senior notes, discount		$ 3.4	$ 3.4
Debt instrument, maturity date		Dec. 15, 2049	Dec. 15, 2049
3.05% Senior Notes, due October 2051 | Senior Notes
Debt Instrument [Line Items]
Stated interest rate	3.05%	3.05%
Senior notes, discount		$ 3.7
Debt instrument, maturity date	Oct. 31, 2051	Oct. 31, 2051

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($) $ in Millions	Oct. 08, 2021	Sep. 21, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Amortization of financing costs			$ 0.5	$ 0.5	$ 1.5	$ 1.5
Long term debt			$ 3,190.4		3,190.4		$ 2,493.7
Debt instrument interest					$ 55.2	$ 56.9
Senior Notes | 3.05% Senior Notes, due October 2051
Debt Instrument [Line Items]
Debt instrument, face amount		$ 700
Stated interest rate		3.05%	3.05%		3.05%
Debt instrument, maturity date		Oct. 31, 2051			Oct. 31, 2051
Long term debt			$ 696.3		$ 696.3		$ 0
Payments of debt issuance costs		$ 7.6
Senior Notes | 4.50% Senior Notes, due November 2023
Debt Instrument [Line Items]
Debt instrument, face amount		$ 700
Stated interest rate		4.50%	4.50%		4.50%
Debt instrument, maturity date		Nov. 1, 2023
Senior Notes | Fixed-Rate Senior Notes
Debt Instrument [Line Items]
Book value of fixed rate debt			$ 3,190.4		$ 3,190.4
Long-term debt (fixed-rate debt), fair value			3,416		$ 3,416
Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, maturity date					Aug. 29, 2021
Debt instrument offering date					Jun. 8, 2021
Letter Of Credit
Debt Instrument [Line Items]
Long term debt			23.5		$ 23.5
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, term					5 years
Long term debt			$ 350		$ 350
Subsequent Events | Senior Notes | 4.50% Senior Notes, due November 2023
Debt Instrument [Line Items]
Stated interest rate	4.50%
Write off amount of remaining balance of unamortized debt issuance costs	$ 1.4
Debt instrument, repurchase amount	769.8
Redemption premium	56.1
Accrued and unpaid interest	$ 13.7

Cash, Cash Equivalents, and M_3

Cash, Cash Equivalents, and Marketable Debt Securities - Schedule of Company's Cash and Available-For-Sale (AFS) Debt Securities by Major Asset Category (Details) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2021		Dec. 31, 2020
Financial Instruments [Line Items]
Adjusted Cost Basis		$ 1,848.9	[1]	$ 1,122.4
Unrealized Gain		0.1	[1]	0.5
Unrealized Loss		0	[1]	0
Fair Value		1,849	[1]	1,122.9
Cash and cash equivalents		1,702.9	[1]	974.6
Short-term marketable debt securities		88.3	[1]	105.6
Long-term marketable debt securities		57.8	[1]	42.7
Level 1
Financial Instruments [Line Items]
Adjusted Cost Basis	[2]	34.6		28.7
Unrealized Gain	[2]	0		0.2
Unrealized Loss	[2]	0		0
Fair Value	[2]	34.6		28.9
Cash and cash equivalents	[2]	7		0.6
Short-term marketable debt securities	[2]	19.3		18.9
Long-term marketable debt securities	[2]	8.3		9.4
Level 2
Financial Instruments [Line Items]
Adjusted Cost Basis	[1]	118.9		123.2
Unrealized Gain	[1]	0.1		0.3
Unrealized Loss	[1]	0		0
Fair Value	[1]	119		123.5
Cash and cash equivalents	[1]	0.5		3.5
Short-term marketable debt securities	[1]	69		86.7
Long-term marketable debt securities	[1]	49.5		33.3
Cash and Cash Equivalents
Financial Instruments [Line Items]
Adjusted Cost Basis		1,695.4		970.5
Unrealized Gain		0		0
Unrealized Loss		0		0
Fair Value		1,695.4		970.5
Cash and cash equivalents		1,695.4		970.5
Short-term marketable debt securities		0		0
Long-term marketable debt securities		0		0
Money Market Fund | Level 1
Financial Instruments [Line Items]
Adjusted Cost Basis	[2]	7		0.6
Unrealized Gain	[2]	0		0
Unrealized Loss	[2]	0		0
Fair Value	[2]	7		0.6
Cash and cash equivalents	[2]	7		0.6
Short-term marketable debt securities	[2]	0		0
Long-term marketable debt securities	[2]	0		0
U.S. Treasury Securities | Level 1
Financial Instruments [Line Items]
Adjusted Cost Basis	[2]	27.6		28.1
Unrealized Gain	[2]	0		0.2
Unrealized Loss	[2]	0		0
Fair Value	[2]	27.6		28.3
Cash and cash equivalents	[2]	0		0
Short-term marketable debt securities	[2]	19.3		18.9
Long-term marketable debt securities	[2]	8.3		9.4
Certificates of Deposit | Level 2
Financial Instruments [Line Items]
Adjusted Cost Basis	[1]	3.9		5.9
Unrealized Gain	[1]	0		0
Unrealized Loss	[1]	0		0
Fair Value	[1]	3.9		5.9
Cash and cash equivalents	[1]	0		1.1
Short-term marketable debt securities	[1]	3.9		4.8
Long-term marketable debt securities	[1]	0		0
Commercial Paper | Level 2
Financial Instruments [Line Items]
Adjusted Cost Basis	[1]			3.2
Unrealized Gain	[1]			0
Unrealized Loss	[1]			0
Fair Value	[1]			3.2
Cash and cash equivalents	[1]			1
Short-term marketable debt securities	[1]			2.2
Long-term marketable debt securities	[1]			0
U.S. Government Agency Securities | Level 2
Financial Instruments [Line Items]
Adjusted Cost Basis	[1]	5.3		6.6
Unrealized Gain	[1]	0		0
Unrealized Loss	[1]	0		0
Fair Value	[1]	5.3		6.6
Cash and cash equivalents	[1]	0		0
Short-term marketable debt securities	[1]	4		2.6
Long-term marketable debt securities	[1]	1.3		4
Corporate Debt Securities | Level 2
Financial Instruments [Line Items]
Adjusted Cost Basis	[1]	109.7		107.5
Unrealized Gain	[1]	0.1		0.3
Unrealized Loss	[1]	0		0
Fair Value	[1]	109.8		107.8
Cash and cash equivalents	[1]	0.5		1.4
Short-term marketable debt securities	[1]	61.1		77.1
Long-term marketable debt securities	[1]	$ 48.2		$ 29.3
[1]	Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.
[2]	Valuations based on quoted prices for identical assets or liabilities in active markets.

Cash, Cash Equivalents, and M_4

Cash, Cash Equivalents, and Marketable Debt Securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financial Instruments [Line Items]
Impairment of marketable debt securities	$ 0	$ 0
Allowance for credit loss	$ 0	$ 0
Minimum
Financial Instruments [Line Items]
Long-term marketable debt securities maturity period	1 year
Maximum
Financial Instruments [Line Items]
Long-term marketable debt securities maturity period	2 years

Cash, Cash Equivalents, and M_5

Cash, Cash Equivalents, and Marketable Debt Securities - Schedule of Marketable Debt Securities in Continuous Loss Position (Details) $ in Millions		Sep. 30, 2021USD ($)Security	Dec. 31, 2020USD ($)Security
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 59.4	$ 48.1
Number of Marketable Debt Securities in a Loss Position | Security		76	62
Unrealized Losses	[1]	$ 0	$ 0
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 50	$ 42.9
Number of Marketable Debt Securities in a Loss Position | Security		63	56
Unrealized Losses	[1]	$ 0	$ 0
U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 0.8	$ 0
Number of Marketable Debt Securities in a Loss Position | Security		2	0
Unrealized Losses	[1]	$ 0	$ 0
U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 8.1	$ 1.7
Number of Marketable Debt Securities in a Loss Position | Security		10	3
Unrealized Losses	[1]	$ 0	$ 0
Certificates of Deposit
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 0.5	$ 1.3
Number of Marketable Debt Securities in a Loss Position | Security		1	2
Unrealized Losses	[1]	$ 0	$ 0
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 0	$ 2.2
Number of Marketable Debt Securities in a Loss Position | Security		0	1
Unrealized Losses	[1]	$ 0	$ 0
[1]	Unrealized losses were insignificant for the periods ended September 30, 2021 and December 31, 2020.

Employee Benefit Plans and Ot_3

Employee Benefit Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Details) - Pension Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.4	$ 5.4	$ 16	$ 17.3
Interest cost	7.4	9.9	22.2	29.8
Expected return on plan assets	(15.8)	(14.2)	(47.3)	(42.6)
Net amortization of unrecognized amounts, Prior service cost	1	1.1	2.9	3.3
Net amortization of unrecognized amounts, Actuarial loss (income)	2.6	2.7	7.8	8.1
Net periodic benefit cost	$ 0.6	$ 4.9	$ 1.6	$ 15.9

Employee Benefit Plans and Ot_4

Employee Benefit Plans and Other Postretirement Benefits - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Plans | Qualified Plan
Pension Contributions [Abstract]
Contributions to pension plan	$ 50	$ 71.4	$ 50	$ 82.5

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - shares	9 Months Ended
	Sep. 30, 2021	May 05, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term equity incentive plan, termination date	May 5, 2030
Number of shares available for future issuance under share-based plan	1,200,000	1,400,000
Number of shares authorized under plan	12,000,000
Performance Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of ROIC as performance measure	50.00%
Percentage of TSR as performance measure	50.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Restricted Stock and Performance Unit Award Activity (Details)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Restricted Stock
Restricted Stock and Performance Units [Roll Forward]
Outstanding at January 1, 2021 | shares	669,102
Granted | shares	173,970
Vested | shares	(164,483)	[1]
Forfeitures | shares	(6,692)
Outstanding at September 30, 2021 | shares	671,897
Restricted Stock and Performance Units (Weighted Average Grant-date Fair Value) [Abstract]
Weighted Average Grant-Date Fair Value, Outstanding at January 1, 2021 | $ / shares	$ 102.55
Weighted Average Grant-Date Fair Value, Granted | $ / shares	134.10
Weighted Average Grant-Date Fair Value, Vested | $ / shares	108.73	[1]
Weighted Average Grant-Date Fair Value, Forfeitures | $ / shares	110.47
Weighted Average Grant-Date Fair Value, Outstanding at September 30, 2021 | $ / shares	$ 109.13
Performance Units
Restricted Stock and Performance Units [Roll Forward]
Outstanding at January 1, 2021 | shares	357,417
Granted | shares	95,236
Vested | shares	(74,894)	[1]
Forfeitures | shares	(19,667)
Outstanding at September 30, 2021 | shares	358,092
Restricted Stock and Performance Units (Weighted Average Grant-date Fair Value) [Abstract]
Weighted Average Grant-Date Fair Value, Outstanding at January 1, 2021 | $ / shares	$ 103.63
Weighted Average Grant-Date Fair Value, Granted | $ / shares	140.47
Weighted Average Grant-Date Fair Value, Vested | $ / shares	134.53	[1]
Weighted Average Grant-Date Fair Value, Forfeitures | $ / shares	132.58
Weighted Average Grant-Date Fair Value, Outstanding at September 30, 2021 | $ / shares	$ 105.38
[1]	Upon vesting of the performance unit awards, PCA issued 81,577 shares, which includes 6,683 shares for dividends accrued during the vesting period.

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Restricted Stock and Performance Unit Award Activity (Parenthetical) (Details) - Performance Units	9 Months Ended
	Sep. 30, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross	81,577
Shares issued on accrued dividends	6,683

Share-Based Compensation - Comp

Share-Based Compensation - Compensation Expense for Share-Based Awards (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 6.8	$ 6	$ 26.9	$ 23.8
Income tax benefit	(1.7)	(1.5)	(6.8)	(6)
Share-based compensation expense, net of tax benefit	5.1	4.5	20.1	17.8
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	3.9	3.2	18.4	16.8
Performance Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 2.9	$ 2.8	$ 8.5	$ 7

Share-Based Compensation - Unre

Share-Based Compensation - Unrecognized Compensation Expense for Share-Based Awards (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 52.2
Remaining weighted-average recognition period	2 years 6 months
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 30.6
Remaining weighted-average recognition period	2 years 7 months 6 days
Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 21.6
Remaining weighted-average recognition period	2 years 3 months 18 days

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, shares in Millions	Sep. 15, 2021	Aug. 25, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Feb. 25, 2016
Common stock dividends paid	$ 95,000,000			$ 284,800,000	$ 224,600,000
Dividends paid per common share (in dollars per share)		$ 1
Stock repurchase program, authorized amount						$ 200,000,000
Repurchases of common stock under stock repurchase program			0	0
Common stock repurchase authorization amount available			$ 193,000,000	$ 193,000,000

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Accumulated Other Comprehensive Income by Component (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 3,246.3
Ending balance	3,608.3
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(0.4)
Other comprehensive income before reclassifications, net of tax	0
Amounts reclassified from AOCI, net of tax	0.4
Ending balance	0
Unfunded Employee Benefit Obligations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(144.2)
Other comprehensive income before reclassifications, net of tax	0
Amounts reclassified from AOCI, net of tax	7.5
Ending balance	(136.7)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(144.5)
Other comprehensive income before reclassifications, net of tax	(0.2)
Amounts reclassified from AOCI, net of tax	7.9
Ending balance	(136.8)
Foreign Exchange Contract | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(0.2)
Other comprehensive income before reclassifications, net of tax	0
Amounts reclassified from AOCI, net of tax	0
Ending balance	(0.2)
Marketable Debt Securities | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0.3
Other comprehensive income before reclassifications, net of tax	(0.2)
Amounts reclassified from AOCI, net of tax	0
Ending balance	$ 0.1

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before taxes		$ 333.9	$ 185.7	$ 828.3	$ 467.3
Income tax benefit		(83.2)	(46.6)	(203.7)	(129.9)
Net income		250.7	139.1	624.6	337.4
Unfunded Employee Benefit Obligations | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service costs	[1]	(0.8)	(1)	(2.5)	(3)
Amortization of actuarial losses	[1]	(2.5)	(2.6)	(7.5)	(7.8)
Income before taxes		(3.3)	(3.6)	(10)	(10.8)
Income tax benefit		0.8	0.9	2.5	2.7
Net income		$ (2.5)	$ (2.7)	$ (7.5)	$ (8.1)
[1]	These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 13, Employee Benefit Plans and Other Postretirement Benefits, for additional information.

Concentrations of Risk - Additi

Concentrations of Risk - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Concentration Risk [Line Items]
Accounts receivable, net, current	$ 1,066.7		$ 832.4
Office Depot | Credit Concentration Risk
Concentration Risk [Line Items]
Accounts receivable, net, current	$ 47.7		$ 39.6
Office Depot | Total Company Sales Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	4.00%	5.00%
Office Depot | Total Company Receivables | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	4.00%		5.00%
Paper | Office Depot | Paper Segment Sales Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	48.00%	43.00%	45.00%

Transactions With Related Par_2

Transactions With Related Parties - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Carrying amount of LTP's assets	$ 8,630.8		$ 8,630.8		$ 7,433.2
Boise Cascade Co-Owner of LTP
Related Party Transaction [Line Items]
Variable interest entity, ownership percentage			50.00%
Boise Cascade Co-Owner of LTP | Fiber
Related Party Transaction [Line Items]
Revenue from related parties	22.3	$ 15.6	$ 63.3	$ 52
Fiber costs from related parties	22.3	15.6	63.3	52
Boise Cascade Co-Owner of LTP | Wood Products, Including Chips and Logs
Related Party Transaction [Line Items]
Fiber costs from related parties	3.6	$ 2.8	$ 10.3	$ 9.5
Packaging Corporation of America
Related Party Transaction [Line Items]
Variable interest entity, ownership percentage			50.00%
Variable Interest Entity
Related Party Transaction [Line Items]
Carrying amount of LTP's assets	2.5		$ 2.5		2.5
Carrying amount of LTP's liabilities	$ 2.5		$ 2.5		$ 2.5

Segment Information - Additiona

Segment Information - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021Segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Selected

Segment Information - Selected Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Net sales	$ 2,000.1	$ 1,693.7	$ 5,687.1	$ 4,944
Operating Income (Loss)	352.8	209.5	885.7	534.7
Non-operating pension income	5	0.6	14.8	1.7
Interest expense, net	(23.9)	(24.4)	(72.2)	(69.1)
Income before taxes	333.9	185.7	828.3	467.3
Trade
Segment Reporting Information [Line Items]
Net sales	2,000.1	1,693.7	5,687.1	4,944
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	(40.9)	(34.3)	(113.2)	(112.9)
Operating Income (Loss)	0	0	0	0
Intersegment Eliminations | Trade
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Operating Segments
Segment Reporting Information [Line Items]
Net sales	2,000.1	1,693.7	5,687.1	4,944
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net sales	(40.9)	(34.3)	(113.2)	(112.9)
Packaging
Segment Reporting Information [Line Items]
Net sales	1,829.4	1,501.1	5,171.4	4,378.5
Operating Income (Loss)	365.2	222.4	940.3	619.9
Packaging | Trade
Segment Reporting Information [Line Items]
Net sales	1,825	1,497.6	5,159.3	4,364.8
Packaging | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	4.4	3.5	12.1	13.7
Packaging | Operating Segments
Segment Reporting Information [Line Items]
Net sales	1,829.4	1,501.1	5,171.4	4,378.5
Paper
Segment Reporting Information [Line Items]
Net sales	150.3	178.1	457.1	518.7
Operating Income (Loss)	11	(7.3)	22.3	(21.7)
Paper | Trade
Segment Reporting Information [Line Items]
Net sales	150.3	178.1	457	518.7
Paper | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	0	0	0.1	0
Paper | Operating Segments
Segment Reporting Information [Line Items]
Net sales	150.3	178.1	457.1	518.7
Corporate and Other
Segment Reporting Information [Line Items]
Net sales	20.4	14.5	58.6	46.8
Operating Income (Loss)	(23.4)	(20.2)	(76.9)	(63.5)
Corporate and Other | Trade
Segment Reporting Information [Line Items]
Net sales	24.8	18	70.8	60.5
Corporate and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Net sales	36.5	30.8	101	99.2
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales	$ 61.3	$ 48.8	$ 171.8	$ 159.7

Segment Information - Selecte_2

Segment Information - Selected Financial Information by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 21, 2021
Segment Reporting Information [Line Items]
Adjustment of asset retirement obligation						$ 9.4
Restructuring charges						0.1
Goodwill impairment charge		$ 0	$ 0			0	$ 55.2
Senior Notes | 3.05% Senior Notes Due October 2051
Segment Reporting Information [Line Items]
Debt Refinancing Cost		$ 0.5				$ 0.5
Stated interest rate		3.05%				3.05%		3.05%
Paper Reporting Unit
Segment Reporting Information [Line Items]
Goodwill impairment charge	$ 55.2			$ 55.2	$ 55.2
Jackson, Alabama Mill | Corrugated Products Facilities
Segment Reporting Information [Line Items]
Adjustment of asset retirement obligation		$ 4.5
San Lorenzo, California [Member]
Segment Reporting Information [Line Items]
Restructuring charges		$ 2.7
San Lorenzo, California [Member] | Packaging and Paper
Segment Reporting Information [Line Items]
Restructuring charges			3.3				24.1
COVID-19 | Packaging and Paper
Segment Reporting Information [Line Items]
Incremental out-of-pocket costs							6.9
Hurricane Laura [Member] | DeRidder Louisiana Mill [Member]
Segment Reporting Information [Line Items]
Restructuring charges			$ 10				$ 10

Commitments, Guarantees, Inde_2

Commitments, Guarantees, Indemnifications, and Legal Proceedings - Additional Information (Details) - DeRidder, Louisiana - USD ($)	3 Months Ended	9 Months Ended
	Jun. 30, 2018	Sep. 30, 2021	Feb. 08, 2017
Schedule Of Commitments And Contingencies [Line Items]
Loss contingency, period of occurrence		February 8, 2017
Liability insurance			$ 1,000,000
Payment of penalties	$ 40,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Events - Advance Packaging Corporation $ in Millions	Oct. 22, 2021USD ($)ft²
Subsequent Event [Line Items]
Payments to acquire assets | $	$ 189
Grand Rapids, Michigan
Subsequent Event [Line Items]
Area of corrugated products facility | ft²	500,000