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Asset Retirement Obligations and Accrued Environmental Costs (Schedule of Change in Overall Asset Retirement Obligation) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at January 1 $ 251 $ 279
Accretion of discount 9 9
Changes in estimates of existing obligations 10 (7)
Spending on existing obligations (15) (20)
Property dispositions (5) (2)
Foreign currency translation (6) (8)
Balance at December 31 $ 244 $ 251