Comcast will announce the spinoff of cable networks Wednesday, sources say

Comcast is moving forward with the spinoff of its cable network channels, people familiar with the matter told CNBC on Tuesday.

The separation is expected to take about a year, and an announcement from the company could come as early as Wednesday, the people said.

The new entity will be led by Mark Lazarus, the current chairman of NBCUniversal's media group, one of the people said. NBCUniversal's Chief Financial Officer Anand Kini, will serve as the CFO and operating chief of the new entity, the person said.

Comcast Chairman and CEO Brian Roberts will maintain a voting position in the company, but will not serve as an officer or on the board of directors, the person added.

The spinoff will be tax free and the share structure of the new entity will mirror that of Comcast's, according to the person.

At NBCUniversal, Donna Langley, the current chief content officer, will become chairman of NBCUniversal Entertainment and Studios, while Matt Strauss, the current head of the direct-to-consumer unit, will be chairman of NBCUniversal Media Group, overseeing sports, ad sales and distribution, the person said. Cesar Conde will remain as NBCUniversal News Group's chairman, including oversight of NBC News Group, while Executive Vice President Adam Miller will become NBCUniversal's Chief Operating Officer, they said.

The company had announced during its quarterly earnings call in October it was considering a split of the cable networks. Comcast President Mike Cavanagh had said the company was exploring creating "a new, well-capitalized company owned by our shareholders and comprised of our strong portfolio of cable networks."

Comcast is moving forward with the decision as millions of customers exit the traditional pay TV bundle in favor of streaming. The company has been beefing up NBCUniversal's streaming platform Peacock in recent years.

Comcast shares were up more than 2% in after hours trading.

The networks that are part of the spinoff also include E!, Syfy, Golf Channel, USA and Oxygen, a person close to the matter said. Bravo will remain part of Comcast's NBCUniversal since its content is heavily featured on Peacock, one of the people said.

Cavanagh had said in October that NBCUniversal's broadcast network NBC and Peacock would remain with Comcast.

Although cord cutting has impacted the business, traditional TV networks remain cash cows for media businesses. Comcast reported in October that third quarter revenue for its media segment, which is mainly comprised of the TV networks, was up nearly 37% to $8.23 billion, largely due to the Olympics. Without the Summer Games, revenue was up almost 5%.

The spinoff will take roughly a year as the company figures out whether licensing agreements need to be put in place, and whether MSNBC and CNBC will continue to work with NBC News, two of the people said.

The spinoff was first reported by The Wall Street Journal.

— CNBC's Julia Boorstin contributed to this article.

This is breaking news. Please refresh for updates.

Disclosure: Comcast owns NBCUniversal, the parent company of CNBC.