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Summary of Significant Accounting Policies - Landfill (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2018
USD ($)
site
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Significant accounting policies      
Receivables related to income tax payments in excess of our provision for income taxes $ 284 $ 504  
Environmental remediation reasonably possible additional losses high estimate 140    
Environmental remediation liabilities 237    
Environmental remediation liabilities not subject to inflation or discounting 35 47  
Increase of environmental remediation liability $ 3 $ 0  
Landfill [Member]      
Significant accounting policies      
Required period to maintain and monitor landfill sites 30 years    
Inflation rate 2.50% 2.50% 2.50%
Credit adjusted, risk free discount rate applicable to long-term asset retirement obligations 5.50%    
Number of landfills sites with expansion | site 15    
Number of expansion landfill sites require CFO approval inclusion of unpermitted airspace | site 2    
Decrease in operating expenses $ (2)   $ (2)
Risk-free discount rate applied to environmental remediation liabilities and recovery assets 2.75% 2.50% 2.50%
Landfill [Member] | Minimum [Member]      
Significant accounting policies      
Permit application process period requirement 1 year    
Landfill [Member] | Maximum [Member]      
Significant accounting policies      
Permit application process period requirement 5 years    
Accounts Receivable Net [Member] | Concentration of Credit Risk [Member] | Maximum [Member]      
Significant accounting policies      
Concentration of risk threshold (as a percent) 5.00% 5.00%