XML 72 R27.htm IDEA: XBRL DOCUMENT v2.4.0.8
Asset Retirement Obligations (Tables)
 6 Months Ended
Jun. 30, 2014
Asset Retirement Obligation [Abstract]  
Asset retirement obligations roll forward

 
Asset Retirement Obligations
 
2014
 
(in millions)
ARO liability at January 1,
$
193.6

Accretion
4.4

Additions(1)
13.2

Revisions
(0.4
)
Liabilities settled(2)
(21.3
)
ARO liability at June 30,
$
189.5