Liabilities for Landfill and Environmental Remediation Costs (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Site Contingency [Line Items]
Total, Environmental Remediation	$ 264
Current (in accrued liabilities)	154	161
Long-term	1,453	1,404
Total	1,607	1,565
Environmental Remediation Liabilities [Member]
Site Contingency [Line Items]
Current (in accrued liabilities), Environmental Remediation	36	38
Long-term, Environmental Remediation	228	235
Total, Environmental Remediation	264	273	284
Landfill Liabilities [Member]
Site Contingency [Line Items]
Current (in accrued liabilities), Landfill	118	123
Long-term, Landfill	1,225	1,169
Total, Landfill Liabilities	$ 1,343	$ 1,292	$ 1,266