CVS Health / Aetna

CVS Health / Aetna wields $372B in revenue and 38M+ members, forged through the 2018 $69B acquisition that created a pharmacy-insurance powerhouse. Employer plans here cost 7% less than the average competitor, translating to $2,100 savings per employee annually. While serving 12M fewer members than UnitedHealth Group, it compensates with a 92% Medicare Advantage retention rate—7 points above the industry norm.