Where can I find a record of the largest providers of robustness insurance within the US?

I'm trying to get a list of the top strength insurance companies in America, broken down by their number of subscribers. Specifically, I am looking for companies that specialize in group plans.
Answers:
don't draw from Blue Cross/Blue Shield. Hospitals nationwide (Atlanta and St. Louis) are dropping them because they refuse to repay bills. They pay less than Medicaid

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