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Summary of Significant Accounting Policies Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2019
Environmental Exit Cost [Line Items]  
Schedule of Asset Retirement Obligations [Table Text Block] The activity in our asset retirement obligation liability for 2019 and 2018 is summarized in the following table.
Dollar amounts in millions
Year ended December 31,
2019
 
2018
Beginning balance
$
12

 
$
11

Accretion expense
1

 
1

Adjusted to expense during the year
(2
)
 
2

Adjusted to other operating credits and charges, net
—

 
(1
)
Ending balance
$
11

 
$
12