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Employee Benefit Plans - Individually Significant Multiemployer Pension Plans (Parenthetical) (Detail)
12 Months Ended
Dec. 31, 2014
Multiemployer Plans [Abstract]  
High end of funded percentage of multiemployer plans in critical status 65.00%wm_HighEndOfFundedPercentageOfMultiemployerPlansInCriticalStatus
High end of funded percentage of multiemployer plans in endangered status 80.00%wm_HighEndOfFundedPercentageOfMultiemployerPlansInEndangeredStatus
Surcharge percentage during first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical 5.00%wm_SurchargePercentageDuringFirstTwelveMonthsOnContributionRatesForPlansCertifiedAsEndangeredSeriouslyEndangeredOrCritical
Period for which surcharge is 5% on contribution rates for plans certified as endangered, seriously endangered or critical 12 months
Surcharge percentage after first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical 10.00%wm_SurchargePercentageAfterFirstTwelveMonthsOnContributionRatesForPlansCertifiedAsEndangeredSeriouslyEndangeredOrCritical
Description of multiemployer defined benefit pension plan A multiemployer defined benefit pension plan that has been certified as endangered, seriously endangered or critical may begin to levy a statutory surcharge on contribution rates. Once authorized, the surcharge is at the rate of 5% for the first 12 months and 10% for any periods thereafter. Contributing employers, however, may eliminate the surcharge by entering into a collective bargaining agreement that meets the requirements of the applicable FIP or RP.
Minimum percentage of total contributions provided by the Company relating to multiemployer plans 5.00%wm_MinimumPercentageOfContributionsProvidedByCompanyRelatingToMultiEmployerPlans