Reclamation and Remediation - Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclamation and remediation expense
Reclamation and remediation	$ 1		$ 6
Accretion expense			68	$ 61
Reclamation and remediation expense	25	$ 20	74	61
Continuing Operations - Operating
Reclamation and remediation expense
Accretion expense	21	18	57	54
Continuing Operations - Non-Operating
Reclamation and remediation expense
Accretion expense	$ 3	$ 2	$ 11	$ 7