Great Plains Energy Inc., the Missouri-based parent company of Kansas City Power & Light, said Tuesday it will acquire Westar Energy Inc. — the biggest utility in Kansas — for approximately $8.6 billion in a cash-and-stock deal.

Under the terms of the agreement, which has been approved by the board of directors of both the companies, Westar’s shareholders will receive $60 per share — $51 in cash and $9 in Great Plains energy stock. This represents a 13 percent premium over Westar’s closing price Friday.

Great Plains, which has a market capitalization of nearly $4.8 billion, will also assume $3.6 billion in Westar’s debt, putting the total value of the deal at nearly $12.2 billion.

“Westar and KCP&L [Kansas City Power & Light] are trusted neighbors and have worked together for generations in Kansas. The combination of our two companies is the best fit for meeting our region’s energy needs,” Terry Bassham, chairman and CEO of Great Plains Energy and KCP&L, said in a statement. “This is an important transaction for Kansas and our entire region. By combining our two companies, we are keeping ownership local and management responsive to regulators, customers and regional needs, while enhancing our ability to build long-term value for shareholders.”

The companies expect the transaction, which is yet to receive regulatory and shareholder approval, to close in the spring of 2017. Once the deal is finalized, Great Plains will have more than 1.5 million customers in Kansas and Missouri.

“Upon completion of the transaction, Bassham will be chairman and chief executive officer of the combined company. In addition, Great Plains Energy will add one director from the Westar Board of Directors to the Great Plains Energy Board of Directors,” the companies said in the statement.

The acquisition comes amid a slowdown in electricity demand across the nation as consumers switch to more energy-efficient appliances. According to Bloomberg, an estimated $52 billion in utility deals, including mergers and acquisitions, were pending or completed in the United States in 2015.

Following the announcement of the deal, Westar’s shares jumped over 9 percent in premarket trade Tuesday while Great Plains shares remained flat.