Aetna Inc. ended its $37 billion takeover of Humana Inc., after deciding not to appeal a ruling by a federal judge who blocked the health insurers' combination on antitrust grounds.

The companies came to a mutual agreement to terminate the deal, and Aetna will pay Humana a $1 billion breakup fee, or about $630 million after taxes. A plan to divest some assets to Molina Healthcare Inc. — a remedy that was rejected by the judge — was also canceled, Aetna said in a statement Tuesday.

Aetna and Humana, which had agreed to combine in July 2015, are free to make new deals or spend billions of dollars on buying back their own shares. Another massive health insurance deal, meanwhile, is grinding forward — for now. Anthem Inc. said on Monday that it's seeking a fast-track appeal of a different judge's ruling that blocked its own proposed $48 billion acquisition of Cigna Corp.