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Note 12 - Commitments and Contingencies (Details) - Asset Retirement Obligation Activity - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Asset Retirement Obligation Activity [Abstract]    
Asset Retirement Obligations at start of period $ 48 $ 43
Liabilities incurred in the current period 3 3
Liabilities settled in the current period (6) (3)
Accretion expense 2 2
Revision in estimated cash flows 1 3
Asset Retirement Obligations at end of period $ 48 $ 48