On Sunday night, MSNBC.com did something that successful Web sites almost never do: it renamed itself.

The site became NBCNews.com, signifying the end of a relationship between NBC and Microsoft that dates back to the earliest days of the commercial Web. Early next year, MSNBC.com will be reborn as a stand-alone site for the cable channel MSNBC, ending the brand confusion that has plagued the site in the past.

With the changes, “we will fully own our digital businesses,” said Steve Capus, the president of NBC News. That’s because the company that controls NBC, Comcast, is acquiring Microsoft’s 50 percent stake in the joint venture that brought MSNBC.com to life in the mid-1990s — in effect, a big investment by Comcast in the news division’s future.

Microsoft is receiving roughly $300 million for the stake, according to people with knowledge of the transaction who insisted on anonymity because the total price was not being made public. A portion of the total price comes from the joint venture’s past profits.