going national, like UHC & Aetna?
Neither of those are true national carriers. Both have specific carriers for states like NY. UHC may also use different carriers (or state specific filings) for WI, MN and MA.
Aetna has roughly half a dozen issuing carriers including . . .
Our family of companies
Aetna Health and Life Insurance Company
Aetna Health Insurance Company
Aetna Life Insurance Company
Accendo Insurance Company
American Continental Insurance Company
Continental Life Insurance Company of Brentwood, Tennessee
Coventry Health and Life Insurance Company
First Health Life and Health Insurance
Regardless of how it all shakes out, it looks like this is going to be a big mess.