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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, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 05, 2018
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Accumulated benefit obligation for plans with obligations in excess of plan assets $ 1,100.0      
Weighted-Average expected return on plan assets for 2019 6.06%      
Pension Contributions [Abstract]        
Expected contribution to qualified plans (at least) $ 15.8      
Company's common stock 1.9 1.8    
Deferred compensation liability $ 14.2 $ 13.6    
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 2019 6.06% 6.55% 6.57%  
Fair value of plan assets $ 873.2 $ 954.8 $ 830.4  
Pension Contributions [Abstract]        
Contributions to pension plan 22.9 43.5    
Pension Plans | Qualified        
Pension Contributions [Abstract]        
Contributions to pension plan 21.8 42.1 57.1  
Matching Contributions        
Pension Contributions [Abstract]        
Company's contribution to defined contribution plans 45.6 42.8 40.4  
Service Related Contributions        
Pension Contributions [Abstract]        
Company's contribution to defined contribution plans $ 24.5 $ 22.4 $ 14.9  
Fixed Income Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Percentage of Fair Value 53.00% 21.00%   52.00%
Other Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Percentage of Fair Value 2.00% 64.00%    
Boise Inc.        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Fair value of plan assets $ 488.9      
Boise Inc. | Equities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 44.00%      
Boise Inc. | Fixed Income Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 54.00%      
Boise Inc. | Other Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 2.00%      
Packaging Corporation of America        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Fair value of plan assets $ 384.3      
Packaging Corporation of America | Equities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 50.00%      
Packaging Corporation of America | Fixed Income Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 49.00%      
Packaging Corporation of America | Other Securities        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Target Allocation 1.00%      
Other(Cash) | Boise Inc.        
Amounts Recognized in Accumulated Other Comprehensive Loss (Income) (Pre-Tax)        
Percentage of Fair Value 100.00%