Avista Corp., the longtime Spokane-based utility once known as Washington Water Power Co., announced this afternoon that Toronto-based Hydro One will acquire it in a transaction valued at $5.3 billion U.S., or $6.7 billion Canadian.

The transaction has been approved by the boards of both companies and is expected to be completed in the second half of 2018.

Avista will maintain its corporate headquarters in Spokane and will continue to operate as a standalone utility serving Washington, Idaho, and Oregon, the company said. As part of that arrangement, the company will maintain its executive team and its own board of directors. The combined company will be headquartered in Toronto.

A release on the transaction said neither Avista nor Hydro One expects workforce reductions as a result of the acquisition.

Combined, the companies will have $25.4 billion U.S. in assets and will serve more than 2 million customers in the Pacific Northwest and Ontario. At that size, the combined company will be one of the 20 largest utilities in North America, they said in the release