Employee Benefit Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost and Other Comprehensive (Income) Loss (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Accumulated losses, excess percentage threshold required on projected benefit obligation	10.00%
Fair value of plan assets at plan year end	$ 267.2	$ 1,100.0
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	6 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