Asset Retirement Obligations Change in Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 123		$ 105
Change in estimated costs	17	[1]	2	[1]
Additions	4		29
Retirements	(22)		(19)
Accretion	5		6
Ending balance	127		123
Reflected as:
Other current liabilities	13		20
Other long-term liabilities	114		103
Total ARO liabilitiy	$ 127		$ 123

[1] Results from changes in the timing and amounts of estimated cash flows for certain plant and mine reclamation.