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Note 1 - Description of Business and Summary of Significant Accounting Policies - Allowance for Credit Losses (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Beginning balance $ 11    
Provision for credit losses 2 $ 11 $ 2
Amounts written off (3)    
Amounts recovered from previous write-offs 0    
Ending balance $ 10 $ 11