Property, Plant and Equipment
Property, plant and equipment are stated at cost. Repair and maintenance costs that do not improve service potential or extend economic life are expensed as incurred. Depreciation is recorded principally by the straight-line method over the estimated useful lives of our assets, which are reviewed periodically and generally have the following ranges: buildings and improvements: 40 years or less; and machinery, equipment and vehicle fleet: 20 years or less. Land is not depreciated, and construction in progress is not depreciated until ready for service. Leasehold improvements are amortized using the straight-line method over the shorter of the remaining lease term, including renewals that are deemed to be reasonably assured, or the estimated useful life of the improvement. Depreciation is not recorded during the period in which a long-lived asset (disposal group) is classified as held for sale, even if the asset (disposal group) continues to generate revenue during the period. Depreciation expense, including the depreciation expense of assets under capital lease, totaled $1,727 million, $1,704 million and $1,654 million in 2013, 2012 and 2011, respectively. Amortization expense for leasehold improvements totaled $16 million, $19 million and $18 million in 2013, 2012 and 2011, respectively.
Certain events or changes in circumstances may indicate that the recoverability of the carrying amount of property, plant and equipment should be assessed, including, among others, a significant decrease in market value, a significant change in the business climate in a particular market, or a current period operating or cash flow loss combined with historical losses or projected future losses. When such events or changes in circumstances are present, we estimate the future cash flows expected to result from the use of the asset (or asset group) and its eventual disposition. These estimated future cash flows are consistent with those we use in our internal planning. If the sum of the expected future cash flows (undiscounted and without interest charges) is less than the carrying amount, we recognize an impairment loss. The impairment loss recognized is the amount by which the carrying amount exceeds the fair value. We use a variety of methodologies to determine the fair value of property, plant and equipment, including appraisals and discounted cash flow models, which are consistent with the assumptions we believe hypothetical marketplace participants would use. Refer to Note 7.
