Property and Equipment
Depreciation expense, computed using the straight-line method, was $1.733 billion in 2013, $1.673 billion in 2012 and $1.461 billion in 2011. Buildings and improvements are depreciated over estimated useful lives ranging generally from 10 to 40 years. Estimated useful lives of equipment vary generally from four to 10 years.
When events, circumstances or operating results indicate the carrying values of certain long-lived assets expected to be held and used, might be impaired, we prepare projections of the undiscounted future cash flows expected to result from the use of the assets and their eventual disposition. If the projections indicate the recorded amounts are not expected to be recoverable, such amounts are reduced to estimated fair value. Fair value may be estimated based upon internal evaluations that include quantitative analyses of revenues and cash flows, reviews of recent sales of similar facilities and independent appraisals.
Long-lived assets to be disposed of are reported at the lower of their carrying amounts or fair value less costs to sell or close. The estimates of fair value are usually based upon recent sales of similar assets and market responses based upon discussions with and offers received from potential buyers.