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Employee Benefit Plans and Other Postretirement Benefits - Additional Information (Details) - USD ($)
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 13, 2017
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Accumulated benefit obligation for plans with obligations in excess of plan assets $ 1,300.0      
Weighted-Average expected return on plan assets for 2020 5.29%      
Pension Contributions [Abstract]        
Expected contribution to qualified plans (at least) $ 19.8      
Company's common stock 1.5 1.9    
Deferred compensation liability $ 17.4 $ 14.2    
Minimum        
Pension Contributions [Abstract]        
Company's contribution to pension plan, percentage 3.00%      
Maximum        
Pension Contributions [Abstract]        
Company's contribution to pension plan, percentage 5.00%      
Pension Plans        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Weighted-Average expected return on plan assets for 2020 6.06% 6.06% 6.55%  
Fair value of plan assets $ 1,073.8 $ 873.2   $ 954.8
Pension Contributions [Abstract]        
Contributions to pension plan 58.9 22.9    
Pension Plans | Qualified        
Pension Contributions [Abstract]        
Contributions to pension plan 57.9 21.8 $ 42.1  
Matching Contributions        
Pension Contributions [Abstract]        
Company's contribution to defined contribution plans 48.9 45.6 42.8  
Service Related Contributions        
Pension Contributions [Abstract]        
Company's contribution to defined contribution plans 27.8 $ 24.5 $ 22.4  
Packaging Corporation of America        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Fair value of plan assets $ 498.8      
Packaging Corporation of America | Equities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 47.00%      
Packaging Corporation of America | Fixed Income Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 52.00%      
Packaging Corporation of America | Other Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 1.00%      
Boise Inc.        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Fair value of plan assets $ 575.0      
Boise Inc. | Equities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 49.00%      
Boise Inc. | Fixed Income Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 49.00%      
Boise Inc. | Other Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 2.00%