Chris Isidore

(CNN Money) -- Anthem, the nation's second-largest health insurer, is now the second-largest company in America with a woman as CEO.

Anthem named Gail Boudreaux to the job on Monday, replacing Joseph Swedish.

The only American company with more revenue and a woman as CEO is General Motors, which has been led by Mary Barra since early 2014. IBM, led by Virginia Rometty, and PepsiCo, led by Indra Nooyi, are the only other U.S. companies among the 50 largest with a woman in charge.

Earlier this year, Fortune magazine counted 32 companies in its Fortune 500 with women as CEOs. But several have given up the top job since then.

Those include Sheri McCoy, who resigned in August as CEO of Avon, and Irene Rosenfeld, who is stepping down this month as CEO of Mondelez International, the maker of Oreos and Cadbury. Yahoo CEO Marissa Mayer left that company after its sale to Verizon.

Boudreaux previously served as CEO of United Healthcare, a subsidiary of UnitedHealth Group, the only insurer larger than Anthem. But she left that company in 2014 and has worked as a consultant to the industry since then. Before United Healthcare, she worked at Blue Cross/Blue Shield and Aetna.

Swedish, 66, who had been CEO and chairman of Anthem, will serve as executive chairman through May. During his tenure, he tried to buy rival Cigna for $54 billion, but that deal was blocked in court on antitrust grounds.