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Note 11 - Commitments and Contingencies (Details) - Asset Retirement Obligation Activity - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Asset Retirement Obligation Activity [Abstract]    
Asset Retirement Obligations at start of period $ 41 $ 48
Liabilities incurred in the current period   1
Liabilities settled in the current period   (9)
Accretion expense   1
Revision in estimated cash flows 1  
Asset Retirement Obligations at end of period $ 42 $ 41