Acquisitions and Divestitures - Pro Forma Consolidated Results of Operations (Detail) (Oakleaf [Member], USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Oakleaf [Member]
Business Acquisition [Line Items]
Operating revenues	$ 13,693	$ 13,059
Net income attributable to Waste Management, Inc.	$ 955	$ 935
Basic earnings per common share	$ 2.03	$ 1.95
Diluted earnings per common share	$ 2.03	$ 1.94