Overview:
UnitedHealth Group is the largest health-insurance & healthcare services company in the U.S. by revenue. ADV Ratings+2managedhealthcareexecutive.com+2
In 2024 it reported revenue of about $400.3 billion. managedhealthcareexecutive.com+1
It serves tens of millions of people through its insurance arm (UnitedHealthcare) plus its services arm (Optum) which covers pharmacy, health-services, data analytics etc. ipmiglobal.com+1
Why it stands out:
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Its scale across insurance + health services gives it a “full-stack” advantage in many markets.
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Its diversified model means it is less purely a traditional insurer and more a broad healthcare enterprise.
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Because of its size and scope, regulatory scrutiny and cost pressures (especially in Medicare/Medicaid and care cost inflation) are material risks.
Key facts:
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Revenue ~ $400 billion (2024). managedhealthcareexecutive.com+1
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It serves more than 50 million people through its insurance business. Statista
Takeaway:
If you’re thinking of the biggest insurance player in the U.S., especially in health, UnitedHealth is it. Their reach, vertical integration, and data/health services components make them more than just an insurer — they’re a major healthcare-services conglomerate.
2. Berkshire Hathaway Inc. (insurance segment)
Overview:
While Berkshire Hathaway is a broad conglomerate, its insurance and reinsurance operations are a massive component of its business and place it among the largest “insurance companies” in the U.S. Brand Vision+1
It is recognized as the largest U.S. insurance-company by assets. ADV Ratings+1
Why it stands out:
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Through its subsidiaries (e.g., GEICO, National Indemnity Company, reinsurers etc.) Berkshire’s insurance operations generate huge “float” (premiums held before claims) which Buffett invests.
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The scale of assets gives it significant financial strength.
Key facts:
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According to one source, assets for Berkshire’s insurance/overall business were about $948.5 billion (U.S. insurance business) in 2024. ADV Ratings+1
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It also owns GEICO, one of the top auto insurers in the U.S.
Takeaway:
Though not solely an “insurance company” in the narrower sense, Berkshire’s insurance operations dominate many insurance metrics (assets, financial strength). If you’re looking at size and influence in U.S. insurance, Berkshire is hard to ignore.
3. The Progressive Corporation
Overview:
Progressive is one of the major property & casualty (P&C) / auto insurers in the U.S., with significant market share in auto insurance. carinsurance.com+1
For example, in the auto insurance space: Progressive held a market share of ~16.74% in 2024 among the largest auto-insurers. carinsurance.com
Why it stands out:
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Strong focus on auto insurance, with innovative pricing, digital tools, and direct consumer channels.
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Significant growth and competitive strength in its segment.
Key facts:
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Revenue: about US$75.37 billion in 2024. Wikipedia
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Among auto insurers: ranked 2nd in market share behind State Farm Mutual Automobile Insurance Company in 2024. carinsurance.com
Takeaway:
If you’re focused on auto or P&C insurance, Progressive is one of the top contenders. It’s less diversified into life/health than some others, but within its specialization it is very influential.