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Landfill and Environmental Costs - Narrative (Details)
$ in Millions, ft³ in Billions
 6 Months Ended
Feb. 06, 2018
USD ($)
Jun. 30, 2018
USD ($)
landfill
ft³
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Environmental Exit Cost [Line Items]          
Number of active solid waste landfills | landfill   194      
Total available disposal capacity (in cubic feet) | ft³   137.7      
Number of closed landfills | landfill   126      
Fair value of assets that are legally restricted for final capping, closure and post-closure obligations   $ 29.0   $ 28.6  
Amount of aggregate potential remediation liability   466.0      
Payments for management and monitoring of remediation area   21.2 $ 23.8    
Remediation liability   555.4 583.6 $ 564.0 $ 602.9
Bridgeton Landfill          
Environmental Exit Cost [Line Items]          
Payments for management and monitoring of remediation area   7.7      
Remediation liability   169.6      
Remediation liability expected to be paid during the remainder of 2018   13.0      
Bridgeton Landfill | Maximum          
Environmental Exit Cost [Line Items]          
Range of loss for remediation costs   $ 177.0      
West Lake Landfill Superfund Site          
Environmental Exit Cost [Line Items]          
Environmental exit costs, anticipated cost $ 236.0        
Environmental exit costs, time period allotted for completion 5 years        
Post-closure costs          
Environmental Exit Cost [Line Items]          
Liabilities from discontinued operations     24.8    
Environmental Restoration Costs          
Environmental Exit Cost [Line Items]          
Liabilities from discontinued operations     $ 6.3