The increase in the fair value of plan assets from contributions made by the employer.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

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Employee Benefit Plans and Other Postretirement Plans - Schedule of Pension Plan Asset Investments and Target Allocations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Company contributions		$ 0.4	$ 30.0
Fair value of plan assets	$ 764.4	$ 805.9
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Fair Value	55.00%	54.00%
International Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Fair Value	22.00%	23.00%
U.S. Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Fair Value	20.00%	20.00%
Real Estate Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Fair Value	1.00%	1.00%
Other Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Fair Value	2.00%	2.00%
Packaging Corporation of America
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 275.2
Packaging Corporation of America \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations	58.00%
Packaging Corporation of America \| Other Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations	3.00%
Packaging Corporation of America \| Equities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations	39.00%
Boise Inc.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 489.2
Boise Inc. \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations	55.00%
Boise Inc. \| Equities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations	45.00%