Landfill and Environmental Remediation Liabilities - Liabilities for Landfill and Environmental Remediation Costs (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Site Contingency [Line Items]
Total, Environmental Remediation	$ 229
Current (in accrued liabilities)	144	$ 147
Long-term	1,605	1,531
Total	1,749	1,678
Landfill [Member]
Site Contingency [Line Items]
Current (in accrued liabilities), Landfill	103	104
Long-term, Landfill	1,417	1,339
Total, Landfill	1,520	1,443	$ 1,421
Environmental Remediation Liabilities [Member]
Site Contingency [Line Items]
Current (in accrued liabilities), Environmental Remediation	41	43
Long-term, Environmental Remediation	188	192
Total, Environmental Remediation	$ 229	$ 235	$ 227