Exelon Corp. won the final regulatory approval needed to complete its $7.3 billion takeover of Constellation Energy Group Inc., forming the largest U.S. electricity marketer. The Federal Energy Regulatory Commission conditionally approved the transaction, according to a filing made public today on the commission’s website. The companies said they will sell three coal-fired power plants in Maryland with 2,648 megawatts owned by Constellation, according to the filing.

Exelon and Constellation also agreed to sell 500 megawatts of fixed-priced electricity contracts until 2015 and bid energy at cost-based rates while asset sales are pending to address market-power concerns, the filing said.