XML 74 R51.htm IDEA: XBRL DOCUMENT v3.10.0.1
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of asset retirement obligations
The components of the change in our asset retirement obligations are shown below:
 
 
Years Ended December 31,
 
 
2018
 
2017
 
 
($ in millions)
Asset retirement obligations, beginning of period
 
$
177

 
$
261

Additions
 
3

 
5

Revisions
 
11

 
(34
)
Settlements and disposals
 
(35
)
 
(70
)
Accretion expense
 
10

 
15

Asset retirement obligations, end of period
 
166

 
177

Less current portion
 
11

 
15

Asset retirement obligation, long-term
 
$
155

 
$
162