Summary of Significant Accounting Policies - Landfill (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) site	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Significant accounting policies
Receivables related to income tax payments in excess of our provision for income taxes	$ 504	$ 352
Environmental remediation liabilities not subject to inflation or discounting	$ 103	$ 90
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	5.75%
Number of landfills sites with expansion | site	15
Number of expansion landfill sites require CFO approval inclusion of unpermitted airspace | site	3
Number of expansion landfill sites require CFO approval inclusion of unpermitted airspace due to opposition | site	1
Number of expansion landfill sites require CFO approval inclusion of unpermitted airspace due to time requirements | site	2
Environmental remediation reasonably possible additional losses high estimate	$ 145
Environmental remediation liabilities	$ 251
Decrease in operating expenses		$ (2)	$ (2)
Risk-free discount rate applied to environmental remediation liabilities and recovery assets	2.50%	2.50%	2.25%
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%