Employee Benefit Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost and Other Comprehensive (Income) Loss (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Accumulated losses, excess percentage threshold required on projected benefit obligation	10.00%
Packaging Corporation of America | Minimum
Defined Benefit Plan Disclosure [Line Items]
Average remaining service period of active employees used for recognition of market-related value of assets	7 years
Packaging Corporation of America | Maximum
Defined Benefit Plan Disclosure [Line Items]
Average remaining service period of active employees used for recognition of market-related value of assets	9 years
Boise Inc. | Minimum
Defined Benefit Plan Disclosure [Line Items]
Average remaining lifetime of inactive participants used for recognition of market-related value of assets	23 years
Boise Inc. | Maximum
Defined Benefit Plan Disclosure [Line Items]
Average remaining lifetime of inactive participants used for recognition of market-related value of assets	26 years