Commitments and Contingencies - Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Accrual for future reclamation costs
Reclamation and remediation obligations	$ 1,774	$ 1,689	$ 1,579	$ 1,611
Current portion of reclamation and remediation liabilities	55	67
Continuing Operations - Non-Operating
Accrual for future reclamation costs
Reclamation and remediation obligations	163	192
Continuing Operations - Operating
Accrual for future reclamation costs
Reclamation and remediation obligations	1,611	1,497
Other current liabilities
Accrual for future reclamation costs
Current portion of reclamation and remediation liabilities	62	83
Other current liabilities | Continuing Operations - Operating
Accrual for future reclamation costs
Current portion of reclamation and remediation liabilities	$ 36	$ 42
Reclamation and remediation liabilities | Continuing Operations - Non-Operating
Accrual for future reclamation costs
Range of reclamation and remediation liabilities upper limit	137.00%
Range of reclamation and remediation liabilities lower limit	0.00%