The U.S. District Court for the District of Columbia in January 2017 found that Aetna’s proposed merger with Humana fell afoul of antitrust laws and ordered it to stop.
According to Judge John Bates, the efficiencies generated by the merger will not be sufficient to mitigate the anti-competitive effects for consumers, specifically in respect of individual Medicare Advantage plans and of individual commercial insurance on the public exchanges in Florida.

Aetna and Humana can still appeal the decision but early indications do not go in that direction.

The opinion is available as a PDF from the U.S. Department of Justice. The press release is here.