Reclamation and Remediation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Reconciliation of Reclamation and Remediation Liabilities
Balance at beginning of period			$ 1,240	$ 1,048
Additions, changes in estimates and other			106	20
Liabilities settled			(57)	(24)
Accretion expense			49	44
Balance at end of period	1,338	1,088	1,338	1,088
Reclamation and Remediation Expenses
Reclamation	0	(9)	0	19
Accretion - operating	14	13	41	38
Accretion - non-operating	3	2	8	6
Reclamation and remediation expense, total	17	6	49	63
Reclamation And Remediation (Textuals) [Abstract]
Accrued for reclamation obligations relating to mineral properties	1,149		1,149		1,070
Accrued obligation associated with former, primarily historic, mining activities	189		189		170
Reclamation and remediation liabilities	$ 62		$ 62		$ 71