Comcast said on Monday that it planned to split off NBCUniversal into a separate company, unwinding a 15-year corporate marriage that put celebrated films and TV shows under the same roof as cable hookups and wireless internet service.

The deal would spin off NBCUniversal — home to “Saturday Night Live,” Universal Pictures, NBC News and Sky — into its own publicly traded company, separate from Comcast, which connects millions of Americans to broadband and traditional television.

The deal, which is expected to be completed in a year, is part of a trend in the media industry of separating faster-growing internet and streaming businesses from cable TV. Earlier this year, Comcast spun off its cable channels, including MS NOW, CNBC and USA, into a separate company, called Versant, part of a bid to streamline its sprawling operations.

Under the terms of the deal, NBCUniversal will be spun off tax-free to Comcast shareholders, with Comcast retaining a 19.9 percent stake for up to one year. Both companies will have the same dual-class stock structure as the combined group does today, which means that the Roberts family and its patriarch, the Comcast chairman, Brian Roberts, is likely to remain in the driver’s seat.

Mr. Roberts said in a statement that the transaction would “unlock a more entrepreneurial management approach” for both companies.

“For more than 60 years, our company has grown by embracing change and investing for the future,” Mr. Roberts and Mike Cavanagh, the co-chief executive of Comcast, said in a memo to employees obtained by The New York Times. “Today is another one of those moments.”

Mr. Roberts will be “actively involved in the leadership” of both companies, according to the announcement. Mr. Cavanagh will become chief executive of NBCUniversal; Michael Angelakis, the former chief financial officer of Comcast, will become Comcast’s chief executive.

Monday’s announcement sent a shock wave through the media industry and raised questions about the future of the renowned film and TV company behind “Saturday Night Live,” “The Office” and “Jurassic Park.” Among them: Could NBCUniversal combine with Versant? Could Comcast sell its remaining stake in NBCUniversal to another media company? And could an independent NBCUniversal become an acquisition target?

Mr. Roberts said on a conference call with analysts Monday that he would not look to sell NBCUniversal or Comcast, and instead aim to grow each business over time.

“This is the right move to put each company in the strongest position to create value.,” Mr. Roberts said.

Comcast’s spinoff of NBCUniversal is the latest in a flurry of deal making in the media and entertainment industry. This month, Fox announced its plans to acquire Roku, the connected TV company known for its distinctive black-and-purple remotes. Paramount, the media company run by the tech scion David Ellison, is closing a deal to acquire Warner Bros. Discovery, the owner of CNN and HBO. The local TV giant Nexstar is in the process of acquiring Tegna, a major station owner.

Comcast’s move will add to the intrigue at the annual Sun Valley Conference, a deal-making hotbed, scheduled for next week.

Monday’s announcement is a sign that Comcast has finally awakened to investor skepticism toward its combination with NBCUniversal, said Rich Greenfield, an analyst at LightShed Partners, in an interview.

“Comcast stock hasn’t moved in 13 years,” he said. “I think this is an admission that the status quo was not working.”

Comcast took control of NBCUniversal in 2011, paying then-owner General Electric $6.2 billion. Two years later, Comcast paid $16.7 billion to acquire the remainder of the company, also buying the NBC studios and offices at 30 Rockefeller Plaza in New York.

Comcast’s union with NBCUniversal reflects the sensibilities of an earlier era, when moguls believed that the producers of film and TV belonged under the same ownership as the companies that delivered content. This often had disastrous results, as when AT&T’s merger with Time Warner resulted in an unwieldy clash of cultures. Comcast’s merger with NBCUniversal was for years held up by analysts as an outlier.

But as the fortunes of traditional media have waned, investors have become wary of such combinations. Comcast’s stock has fallen steadily over the past five years, along with much of the rest of the media industry; it jumped more than 20 percent in premarket trading on Monday.