Variable Interest Entities - Additional Information (Detail) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			9 Months Ended					9 Months Ended		1 Months Ended			1 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2012 Limited Liability Company II [Member]	Sep. 30, 2012 Limited Liability Company [Member]	Sep. 30, 2012 Limited Liability Company [Member] Limited Liability Company II [Member] USD ($)	Dec. 31, 2011 Limited Liability Company [Member] Limited Liability Company II [Member] USD ($)	Dec. 31, 2000 Limited Liability Company [Member] Limited Liability Company II [Member] USD ($)	Sep. 30, 2012 Investment in Recycling and Waste to Energy USD ($)	Sep. 30, 2012 Investment in Recycling and Waste to Energy GBP (£)	Jan. 31, 2011 Investment in Refined Coal Facility [Member] USD ($)	Sep. 30, 2012 Investment in Refined Coal Facility [Member] USD ($)	Dec. 31, 2011 Investment in Refined Coal Facility [Member] USD ($)	Apr. 30, 2010 Low-Income Housing Properties [Member] USD ($)	Sep. 30, 2012 Low-Income Housing Properties [Member] USD ($)	Dec. 31, 2011 Low-Income Housing Properties [Member] USD ($)
Variable Interest Entity [Line Items]
Percentage of ownership in LLC's						0.25%	0.50%				50.00%	50.00%
Percentage of variable interest entities owned by other companies						99.75%	99.50%
Total initial investment by other companies										$ 167
Under the LLC agreements, the LLC shall be dissolved upon the occurrence of any of the following events			(i) a written decision of all members of the LLCs; (ii) December 31, 2063; (iii) a court's dissolution of the LLCs; or (iv) the LLCs ceasing to own any interest in the waste-to-energy facilities.
Reporting entity percentage of interest in earnings of variable interest entity after achieving targeted returns								80.00%
Other companies percentage of interest in earnings of variable interest entity after achieving targeted returns								20.00%
Consolidated variable interest entity carrying amount of asset								299	308
Noncontrolling interests	324		324		320			250	246
Expense recognized for other companies' noncontrolling interests in LLCs earnings	9	13	34	38
Expected cost to construct Waste-to-Energy LLC facility											323	200
Total commitment											92	57
Note receivables balance from the LLC											11	7
Investment balance											1			27	35		160	178
Cash payments to acquire equity method investment													48			6
Consideration for investment																221
Value of notes payable included in consideration for investment																215
Equity method investments debt balance																	158	176
Variable interest entities primary beneficiary trust fair value assets	121		121		123
Carrying value of restricted trust funds and escrow accounts for which company is not the sole beneficiary specifically for future settlement of landfill and environmental remediation liabilities	$ 111		$ 111		$ 107