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Schedule of Change in Asset Retirement Obligations (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Asset Retirement Obligation Disclosure [Abstract]      
Asset Retirement Obligation $ 87 $ 64 $ 63
Asset Retirement Obligation, Liabilities Incurred 0 1 1
Asset Retirement Obligation, Liabilities Settled (3) (4) (3)
Asset Retirement Obligation, Accretion Expense 6 4 4
Asset Retirement Obligation, Revision of Estimate (4) (22) (1)
Asset Retirement Obligation $ 94 $ 87 $ 64