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.

NorthWestern Energy Group and Black Hills have agreed to combine to form a large $7.8 billion regulated electric and natural gas utility company at a time of climbing energy demand across the U.S.

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