Comcast Corp., in a bullish bet on traditional entertainment, is buying General Electric Co.'s 49% stake in NBCUniversal for $16.7 billion, giving the cable operator full ownership of the film and television giant much sooner than expected.

Two years ago Comcast bought an initial 51% stake in NBCU, transforming the nation's biggest cable operator into a diversified media company. Now, Comcast is doubling down, despite the uncertainty facing the industry, given the rise of digital outlets like Netflix Inc. and Amazon.com...