Contract Amortization Revenue
Contract amortization represents the roll-off of in-market customer contracts valued under purchase accounting and the favorable change of $18 million, as compared to 2013, related primarily to the completion of the roll-off of certain customer contracts acquired in the Reliant acquisition.
Depreciation and Amortization Expense
Depreciation and amortization expense increased by $267 million for the year ended December 31, 2014, compared to the same period in 2013, due primarily to the EME acquisition in April 2014, the Alta Wind acquisition in August 2014 and additional depreciation expense of $110 million as a result of El Segundo, Marsh Landing and Ivanpah reaching commercial operations in late 2013.
In 2014, the Company recorded impairment losses of $97 million related primarily to the Osceola and Coolwater facilities as further described in Item 15 - Note 10, Asset Impairments, to the Consolidated Financial Statements.
In the fourth quarter of 2013, the Company recorded an impairment loss of $459 million related to the Indian River facility. The impairment loss resulted from a change in management's long-term view on the economics of the facility, as further described in Item 15 — Note 10, Asset Impairments, to the Consolidated Financial Statements.
Selling, Marketing, General and Administrative Expenses
Selling, marketing, general and administrative expenses are comprised of the following:
For the year ended December 31,
Selling and marketing expense
General and administrative expenses
Selling and marketing expense increased $31 million for the year ended December 31, 2014, compared to the same period in 2013, due primarily to the acquisitions of RDS and Pure Energies, which provided NRG Home Solar with an installation team, internet, and telephonic sales team and certain sales channels.
General and administrative expenses increased $101 million for the year ended December 31, 2014, compared to the same period in 2013, due in part to the acquisition of EME in April 2014 and the expansion of the NRG Home Solar business as well as the presentation of NRG Home Solar expenses as development in 2013.
Acquisition-related Transaction and Integration Costs
NRG incurred transaction and integration costs of $84 million for the year ended December 31, 2014, compared to $128 million for the same period in 2013. The reduction in transaction and integration costs is due primarily to the substantial completion of the GenOn integration activities in 2013, offset by the acquisitions and integration costs of Alta Wind, Dominion, and EME in 2014.
NRG incurred development costs of $91 million for the year ended December 31, 2014, compared to $84 million for the same period in 2013. This increase in development costs relates primarily to an increase in Renewable development expenses.
Equity in Earnings of Unconsolidated Affiliates
NRG's equity in earnings of unconsolidated affiliates was $38 million for the year ended December 31, 2014, compared to $7 million for the same period in 2013. The increase was due primarily to $13 million of income in 2014 from a long-term natural gas hedge entered into by Saguaro in July 2013 compared to losses of $11 million in 2013, and $13 million resulting from the acquisition of EME in April 2014.