There are a number of ways to rank the size of insurance companies. Companies can be measured by their market capitalization (the value of the company on a stock exchange) or by using sales figures, such as net premiums written in a year or how many policies were sold.
Largest by Market Capitalization
Investors can buy shares of publicly traded companies in the insurance industry. The largest insurance companies as of 2018 by market capitalization on the world stock exchanges were:
Non-health Insurance Companies:
Company Name | Market Capitalization |
Berkshire Hathaway ( BRK.A) |
$308 billion |
China Life Insurance(LFC) | $80  billion |
Allianz (AZSEY) | $76.8 billion |
American International Group (AIG) | $72.3 billion |
Ping An of China (PNGAY) | $65.6 billion |
MetLife (MET) | $59.4 billion |
AXA ( AXA) |
$57.8 billion |
AIA Group Hong Kong (AAIGF) | $54.4 billion |
ING Groep (ING) | $54.4 billion |
Zurich Insurance (ZURVY) | $45.4 Billion |
(Source: Thompson Reuters)
Health Insurance and Managed Health Care Companies:
Company Name                 |   Market Capitalization |
United Healthcare (UNH) | $91.8 billion |
Wellpoint ( WLP) |
$34.3 billion |
Aetna (AET) | $29.8 billion |
CIGNA Corp. (CI) | $26.8 billion |
Humana (HUM) | $21.1Â billion |
Centene Corp. (CNC) | $5.7 billion |
Health Net, Inc. ( HNT) |
$3.9 billion |
WellCare Health Plans (WCG) | $3.1 billion |
Healthspring ( HS) |
$3.7 billion |
Molina Healthcare (MOH) | $2.4 billion |
(Source: Thompson Reuters)
Not all insurance companies are publicly traded. In fact, many insurers are structured as mutual companies where policy holders of participating policies are essentially partial owners of the company. The mutual company model for an insurance company dates back hundred of years, and there are certain benefits conferred on policyholders that do not exist with publicly traded (stock company) insurers.
Largest Insurance Companies by Sales and Product Line
It is useful to differentiate between the type of insurance, or line, that is being considered when considering the largest insurance companies. Using sales data is helpful as some of the largest insurance companies in the United States are not publicly traded and therefore their market value is not easily ascertained.
Property & Casualty
Property casualty insurers write policies covering property such as real estate, dwellings, cars and other vehicles. They also write policies dealing with liabilities that may be incurred by accident or negligence related to those properties to defray the cost of lawsuits or medical damages resulting from such incidents.
The top U.S. property casualty companies in 2018 by net premiums written (the amount of money that non-life policies can expect to receive over the life of the contract, less commissions and costs) are:
Company | Â Net Premiums Written |
State Farm Group | $64.6 billion |
Berkshire Hathaway (BRK.A) | $46.0 billion |
Allstate Insurance Group (ALL) | $30.6 billion |
Liberty Mutual | $28.6 billion |
Progressive Insurance Group (PGR) | $27.1 billion |
Travelers Group (TRV) | $24.5 billion |
USAA Group | $19.6 billion |
Nationwide Group | $18.8 billion |
Farmers Insurance Group | $14.3 billion |
American International Group (AIG) | $14.2 billion |
(Source A.M. Best)
Life Insurance Companies
Life Insurance companies promise to pay out a lump sum benefit upon the death of the insured. Although actuarial science has created mortality tables to accurately estimate the future liability of policies to be paid, having financial strength ensures that these companies can meet all of their obligations while still earning a profit.
Life Insurance companies in the U.S. can be ranked by direct premium written (the amount of new policies written directly and not re-insured). For 2018:
 Company |  Total Direct Premium |  Market Share |
Metropolitan Group (MET) | $12.6 billion | 7.87% |
Northwestern Mutual | $10.1 billion | 6.29% |
New York Life Group | $8.8 billion | 5.48% |
Prudential of America (PRU) | $8.6 billion | 5.33% |
Lincoln National | $6.9 billion | 4.30% |
MassMutual | $6.6 billion | 4.15% |
Aegon (AEG) | $4.6 billion | 2.90% |
John Hancock | $4.4 billion | 2.84% |
State Farm | $4.0 billion | 2.73% |
Guardian Life Insurance Co. | $3.8 billion | 2.38% |
(Source:Â NAIC)
Health Insurance Companies
Health insurance companies provide policies to cover all or part of policyholder’s health and medical costs. Policies may be purchased individually or through an employer. Technically, the United States government is the largest health insurance provider in America through the Medicare program, Social Security and with Medicaid administered by individual states.
The largest non-government sponsored U.S. health insurance companies measured by total direct premium collected in 2016 was:
Company | Total Direct Premium | Market Share |
UnitedHealth Group (UNH) | $125 billion | 12.90% |
Kaiser Foundation Group | $72.6 billion | 7.46% |
Anthem Inc Group | $59.8 billion | 6.15% |
Aetna Group (AET ) |
$54.3 billion | 5.58% |
Humana Group | $53.8 billion | 5.53% |
HCSC Group | $32.3 billion | 3.31% |
Centene Corp Group | $25.7 billion | 2.64% |
Cigna Health Group (CI) | $24.0 billion | 2.47% |
Molina Healthcare Inc Group | $17.8 billion | 1.83% |
Independence Health Group Inc Group | $17.0 billion | 1.75% |
(Source: NAIC. Note: The sales data on insurance companies is from 2016, the last year of available data.)
The Bottom Line
Ranking the largest insurance companies can be done in a number of ways. Shares of publicly traded companies can be bought to help build a well-diversified investment portfolio that has exposure to the financial and healthcare sectors. Identifying which types of insurance a company primarily deals with helps determine which firms are competitors and which really are not. Looking at sales figures, or premiums collected in a year, one can also see how public companiesstack up against privately held or mutual companies which make up a large segment of the industry.