Black Hills and NorthWestern Energy said on Tuesday they would merge, creating a $15.4 billion regulated electric and natural gas utility better equipped to invest in grid infrastructure and meet rising U.

The utility will have a market capitalization of approximately $7.8 billion, based on each company’s closing stock price as of Monday.

Black Hills and NorthWestern Energy have entered a definitive agreement that will establish a electric and natural gas utility company.