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Asset Retirement Obligation (Tables)
 12 Months Ended
Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Asset Retirement Obligations [Table Text Block]
The following table presents amounts recognized related to asset retirement obligations for the periods indicated (in millions):
 
 
2019
 
2018
Balance at January 1
 
$
415

 
$
368

Additional liabilities incurred
 
19

 
19

Liabilities settled
 
(12
)
 
(14
)
Accretion expense
 
21

 
18

Change in estimated cash flows
 
58

 
24

Sale of plants
 
(71
)
 
—

Other
 
(2
)
 
—

Balance at December 31
 
$
428

 
$
415