At December 31, 2018, our recorded goodwill was $1,126 million, approximately 48 percent of which resided in the automated transmissions reporting unit, 34 percent in the aggregated emission solutions and filtration reporting unit, 8 percent in the electrified power reporting unit and 7 percent in the distribution reporting unit. Changes in our projections or estimates, a deterioration of our operating results and the related cash flow effect or a significant increase in the discount rate could decrease the estimated fair value of our reporting units and result in a future impairment of goodwill. See NOTE 8, "GOODWILL AND OTHER INTANGIBLE ASSETS," for additional information.
Other Intangible Assets
We capitalize other intangible assets, such as trademarks, patents and customer relationships, that have been acquired either individually or with a group of other assets. These intangible assets are amortized on a straight-line basis over their estimated useful lives generally ranging from 3 to 25 years. Intangible assets are reviewed for impairment when events or circumstances indicate that the carrying value may not be recoverable over the remaining lives of the assets. See NOTE 8, "GOODWILL AND OTHER INTANGIBLE ASSETS," for additional information.
We capitalize software that is developed or obtained for internal use. Software costs are amortized on a straight-line basis over their estimated useful lives generally ranging from 3 to 12 years. Software assets are reviewed for impairment when events or circumstances indicate that the carrying value may not be recoverable over the remaining lives of the assets. Upgrades and enhancements are capitalized if they result in significant modifications that enable the software to perform tasks it was previously incapable of performing. Software maintenance, training, data conversion and business process reengineering costs are expensed in the period in which they are incurred. See NOTE 8, "GOODWILL AND OTHER INTANGIBLE ASSETS," for additional information.
We charge the estimated costs of warranty programs, other than product campaigns, to cost of sales at the time products are sold and revenue is recognized. We use historical experience to develop the estimated liability for our various warranty programs. Factors considered in developing these estimates included component failure rates, repair costs and the point of failure within the product life cycle. As a result of the uncertainty surrounding the nature and frequency of product campaigns, the liability for such campaigns is recorded when we commit to a recall action or when a recall becomes probable and estimable, which generally occurs when it is announced. The liability for these campaigns is reflected in the provision for warranties issued. We review and assess the liability for these programs on a quarterly basis. We also assess our ability to recover certain costs from our suppliers and record a receivable when we believe a recovery is probable. In addition to costs incurred on warranty and product campaigns, from time to time we also incur costs related to customer satisfaction programs for items not covered by warranty. We accrue for these costs when agreement is reached with a specific customer. These costs are not included in the provision for warranties, but are included in cost of sales. In addition, we sell extended warranty coverage on most of our engines. See Extended Warranty policy discussion above and NOTE 9, "PRODUCT WARRANTY LIABILITY," for additional information.
Research and Development
Our research and development program is focused on product improvements, product extensions, innovations and cost reductions for our customers. Research and development expenditures include salaries, contractor fees, building costs, utilities, testing, technical IT, administrative expenses and allocation of corporate costs and are expensed, net of contract reimbursements, when incurred. From time to time, we enter into agreements with customers and government agencies to fund a portion of the research and development costs of a particular project. We generally account for these reimbursements as an offset to the related research and development expenditure. Research and development expenses, net of contract reimbursements, were $894 million, $734 million and $616 million for the years ended December 31, 2018, 2017 and 2016, respectively. Contract reimbursements were $120 million, $137 million and $131 million for the years ended December 31, 2018, 2017 and 2016, respectively.
Related Party Transactions
In accordance with the provisions of various joint venture agreements, we may purchase products and components from our joint ventures, sell products and components to our joint ventures and our joint ventures may sell products and components to unrelated parties. Joint venture transfer prices may differ from normal selling prices. Certain joint venture agreements transfer product at cost, some transfer product on a cost-plus basis, and others transfer product at market value. Our related party sales are presented on the face of our Consolidated Statements of Income. Our related party purchases were not material to our financial position or results of operations.