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Summary of Significant Accounting Policies - Landfill (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) item site	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant accounting policies
Number of expansion landfill sites require CFO approval inclusion of unpermitted airspace | item	2
Environmental remediation reasonably possible additional losses high estimate	$ 140
Environmental remediation liabilities	230
Environmental remediation liabilities not subject to inflation or discounting	34	$ 36
Increase (decrease) in environmental remediation liabilities	$ (12)	$ (8)
Landfill [Member]
Significant accounting policies
Inflation rate	2.25%	2.50%	2.50%
Credit adjusted, risk free discount rate applicable to long-term asset retirement obligations	5.00%
Number of landfills sites with expansion | site	15
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%
Environmental Remediation Liabilities [Member]
Significant accounting policies
Environmental remediation liabilities	$ 230	$ 240
Increase (decrease) in operating expenses	$ 8	$ 9	$ (2)
Risk-free discount rate applied to environmental remediation liabilities and recovery assets	1.00%	1.75%	2.75%

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Environmental Remediation Liabilities That Have Never Been Subject To Inflation Or Discounting

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Number of landfill sites with expansions that require the Chief Financial Officer to approve the inclusion of the unpermitted airspace.

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Number Of Landfills Sites With Expansion

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Significant Accounting Policies [Line Items]

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Weighted average rate applicable to asset retirement obligations.

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