Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended															12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net																$ (88.4)	[1]	$ (58.3)	[2],[3]	$ (62.9)	[4]
Income before taxes																614.3		423.6	[3]	374.7
(Provision) benefit for income taxes																(221.7)		17.7		(214.5)
Net income	98.5	[5]	104.4	[6]	99.6	[7]	90.1	[8]	228.1	[9]	84.7	[10]	66.2	[11]	62.3	392.6		441.3		160.2
Unfunded Employee Benefit Obligations | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service cost																(6.3)	[12]	(5.8)	[12]
Amortization of actuarial gain / (losses)																(0.7)	[12]	(5.2)	[12]
Curtailment loss																0	[12]	(10.9)	[12]
Income before taxes																(7.0)		(21.9)
(Provision) benefit for income taxes																2.8		8.5
Net income																(4.2)		(13.4)
Treasury Lock | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense, net																(5.7)	[13]	(5.7)	[13]
(Provision) benefit for income taxes																2.2		2.2
Net income																$ (3.5)		$ (3.5)

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

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

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

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

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

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

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

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

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

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

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

[12] These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 11, Employee Benefit Plans and Other Postretirement Benefits, for additional information.

[13] This AOCI component is included in interest expense, net. Amount relates to the amortization of the effective portion of treasury lock derivative instruments recorded in AOCI. The net amount of settlement gains or losses on derivative instruments included in AOCI to be amortized over the next 12 months is a net loss of $5.7 million ($3.4 million after-tax). For a discussion of treasury lock derivative instrument activity, see Note 13, Derivative Instruments and Hedging Activities, for additional information.