Property, Plant and Equipment
Property, plant and equipment are carried at cost. Depreciation and amortization are provided by the straight-line method over the estimated useful lives of the assets, which are as follows: Vehicles—6 to 15 years; Aircraft—12 to 30 years; Buildings—20 to 40 years; Leasehold Improvements—lesser of asset useful life or lease term; Plant Equipment—6 to 8.25 years; Technology Equipment—3 to 5 years. The costs of major airframe and engine overhauls, as well as routine maintenance and repairs, are charged to expense as incurred.
Interest incurred during the construction period of certain property, plant and equipment is capitalized until the underlying assets are placed in service, at which time amortization of the capitalized interest begins, straight-line, over the estimated useful lives of the related assets. Capitalized interest was $14, $18 and $17 million for 2013, 2012, and 2011, respectively.
We review long-lived assets for impairment when circumstances indicate the carrying amount of an asset may not be recoverable based on the undiscounted future cash flows of the asset. If the carrying amount of the asset is determined not to be recoverable, a write-down to fair value is recorded. Fair values are determined based on quoted market values, discounted cash flows, or external appraisals, as applicable. We review long-lived assets for impairment at the individual asset or the asset group level for which the lowest level of independent cash flows can be identified.
