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Supplemental Balance Sheet Information (Tables)
 6 Months Ended
Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Schedule of inventories
Total inventories consisted of the following:
(millions)
June 30, 2015
 
December 31, 2014
Finished goods
$
218

 
$
232

Work in progress
36

 
35

Raw materials
70

 
62

Total
$
324

 
$
329
Changes in the liability for asset retirement obligations
Changes in the liability for asset retirement obligations consisted of the following:
 
Six months ended June 30,
(millions)
2015
 
2014
Balance as of January 1
$
123

 
$
132

Accretion expense
4

 
4

Liabilities incurred
—

 
—

Changes in estimated cash flows (a)
(1
)
 
(10
)
Liabilities settled
(1
)
 
(2
)
Foreign currency translation
(2
)
 
(1
)
Balance as of June 30
$
123

 
$
123

(a)
Changes in estimated cash flows for the six months ended June 30, 2014 included changes in estimates primarily for our gypsum quarry and ship loading facility in Windsor, Nova Scotia, Canada, which we permanently closed during the third quarter of 2011, and our mining operation in Little Narrows, Nova Scotia, Canada as a result of receiving regulatory approval of a revised reclamation plan in 2014.