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Note 9 - Commitments and Contingencies (Details) - Asset Retirement Obligation Activity - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation Activity [Abstract]    
Asset Retirement Obligations at start of period $ 47 $ 53
Liabilities incurred in the current period 2 1
Liabilities settled in the current period (7) (3)
Accretion expense 2 2
Revision in estimated cash flows (1) (6)
Asset Retirement Obligations at end of period $ 43 $ 47