Cigna Group walked away from talks with Humana Inc., putting an early end to what would have been one of the biggest deals of the decade.

Cigna ended the discussions after failing to agree with Humana on price, a task made more difficult as Cigna's shares declined, according to people with knowledge of the matter. That obstacle proved to be too high, even though the two sides believed a merger made strategic sense and thought it could clear regulatory hurdles, said the people, who asked not to be identified because the information was private.

A combination would have created a health insurance behemoth with a market value of about $135 billion, even after share price declines for both companies in the past month. The bearish market response signaled that investors thought a combination might have been worth less than the sum of its parts.