MidAmerican Energy Holdings Co., a subsidiary of Berkshire Hathaway Inc., and NV Energy Inc. announced Wednesday that they have reached a definitive agreement for MidAmerican to acquire NV Energy. Based in Las Vegas, NV Energy is an energy holding company serving approximately 1.3 million electric and natural gas customers. The transaction, which has been unanimously approved by both companies' boards of directors, has an enterprise value of approximately $10 billion. When the transaction is completed, probably in the first quarter of 2014, Des Moines-based MidAmerican will have assets of approximately $66 billion, and its regulated electric and gas utilities will serve 8.4 million customers.