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Note 11 - Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]  
Asset Retirement Obligation Activity

The following table provides asset retirement obligation activity (in millions):

 

 

 

For the Year Ended December 31,

 

 

 

2021

 

 

2020

 

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