the analysis of our depreciation studies . changes in the estimated service lives of our assets and their related depreciation rates are implemented prospectively . under group depreciation , the historical cost ( net of salvage ) of depreciable property that is retired or replaced in the ordinary course of business is charged to accumulated depreciation and no gain or loss is recognized . the historical cost of certain track assets is estimated using ( i ) inflation indices published by the bureau of labor statistics and ( ii ) the estimated useful lives of the assets as determined by our depreciation studies . the indices were selected because they closely correlate with the major costs of the properties comprising the applicable track asset classes . because of the number of estimates inherent in the depreciation and retirement processes and because it is impossible to precisely estimate each of these variables until a group of property is completely retired , we continually monitor the estimated service lives of our assets and the accumulated depreciation associated with each asset class to ensure our depreciation rates are appropriate . in addition , we determine if the recorded amount of accumulated depreciation is deficient ( or in excess ) of the amount indicated by our depreciation studies . any deficiency ( or excess ) is amortized as a component of depreciation expense over the remaining service lives of the applicable classes of assets . for retirements of depreciable railroad properties that do not occur in the normal course of business , a gain or loss may be recognized if the retirement meets each of the following three conditions : ( i ) is unusual , ( ii ) is material in amount , and ( iii ) varies significantly from the retirement profile identified through our depreciation studies . a gain or loss is recognized in other income when we sell land or dispose of assets that are not part of our railroad operations . when we purchase an asset , we capitalize all costs necessary to make the asset ready for its intended use . however , many of our assets are self-constructed . a large portion of our capital expenditures is for replacement of existing track assets and other road properties , which is typically performed by our employees , and for track line expansion and other capacity projects . costs that are directly attributable to capital projects ( including overhead costs ) are capitalized . direct costs that are capitalized as part of self- constructed assets include material , labor , and work equipment . indirect costs are capitalized if they clearly relate to the construction of the asset . general and administrative expenditures are expensed as incurred . normal repairs and maintenance are also expensed as incurred , while costs incurred that extend the useful life of an asset , improve the safety of our operations or improve operating efficiency are capitalized . these costs are allocated using appropriate statistical bases . total expense for repairs and maintenance incurred was $ 2.3 billion for 2013 , $ 2.1 billion for 2012 , and $ 2.2 billion for 2011 . assets held under capital leases are recorded at the lower of the net present value of the minimum lease payments or the fair value of the leased asset at the inception of the lease . amortization expense is computed using the straight-line method over the shorter of the estimated useful lives of the assets or the period of the related lease . 12 . accounts payable and other current liabilities dec . 31 , dec . 31 , millions 2013 2012 .
what was the average repairs and maintenance incurred from 2011 to 2013 in billions
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