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Acquisitions and Divestitures - Pro Forma (Detail) - Advanced Disposal [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Business Acquisition [Line Items] |  |
Operating revenues | $ 16,192 | $ 16,660
Net income attributable to Waste Management, Inc. | $ 1,685 | $ 1,472
Basic earnings per common share | $ 3.99 | $ 3.47
Diluted earnings per common share | $ 3.96 | $ 3.44
Weighted average common shares outstanding: |  |
Basic (in shares) | 423 | 425
Diluted (in shares) | 425 | 428

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