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Asset Retirement Obligations, Activity Related to Asset Retirement Obligations (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Activity related to asset retirement obligations [Roll Forward]    
Balance, beginning of period $ 76 $ 81
Accretion expense 1 1
Remeasurement/translation 3 4
Changes in estimates, including cost and timing of cash flows 0 1
Settlements/payments (1) 0
Balance, end of period $ 79 $ 87