Earnings Per Share - Computation of Basic and Diluted Income Per Common Share (Details) (USD $) In Millions, except Per Share data, 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
Numerator:
Net income	$ 98.5	[1]	$ 104.4	[2]	$ 99.6	[3]	$ 90.1	[4]	$ 228.1	[5]	$ 84.7	[6]	$ 66.2	[7]	$ 62.3	$ 392.6	$ 441.3	$ 160.2
Less: distributed and undistributed earnings allocated to participating securities																(5.7)	0	0
Net income attributable to common shareholders																$ 386.9	$ 441.3	$ 160.2
Denominator:
Weighted average basic common shares outstanding																97.0	96.6	96.4
Effect of dilutive securities																0.1	0.9	1.1
Diluted common shares outstanding																97.1	97.5	97.5
Basic income per common share	$ 1.00	[1]	$ 1.06	[2]	$ 1.01	[3]	$ 0.92	[4]	$ 2.36	[5]	$ 0.88	[6]	$ 0.69	[7]	$ 0.65	$ 3.99	$ 4.57	$ 1.66
Diluted income per common share	$ 1.00	[1]	$ 1.06	[2]	$ 1.01	[3]	$ 0.92	[4]	$ 2.34	[5]	$ 0.87	[6]	$ 0.68	[7]	$ 0.64	$ 3.99	$ 4.52	$ 1.64

[1] 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).

[2] 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).

[3] 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).

[4] 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).

[5] 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).

[6] 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).

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