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Summary of Significant Accounting Policies - Summary of Revisions in Risk-Free Discount Rate Applied to Environmental Remediation Liabilities and Recovery Assets (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounting Policies [Abstract]      
Charge (reduction) to Operating expenses $ 10wm_IncreaseDecreaseToOperatingExpensesDueToChangeInDiscountRateUsedToEstimatePresentValueOfEnvironmentalRemediationObligationsAndRecoveryAssets $ (13)wm_IncreaseDecreaseToOperatingExpensesDueToChangeInDiscountRateUsedToEstimatePresentValueOfEnvironmentalRemediationObligationsAndRecoveryAssets $ 3wm_IncreaseDecreaseToOperatingExpensesDueToChangeInDiscountRateUsedToEstimatePresentValueOfEnvironmentalRemediationObligationsAndRecoveryAssets
Risk-free discount rate applied to environmental remediation liabilities and recovery assets 2.00%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate 3.00%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate 1.75%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate