There are a number of ways to rank the size of insurance companies such as property, casualty or total market capital. Here onlinestudybook.com listed Companies on the based on market capitalization.

The list is given bellow —

1. State Farm 
Direct Premiums Written: $64.8 billion
Market Share: 10.1%


2. Berkshire Hathaway 
Direct Premiums Written: $38.4 billion
Market Share: 6.0%

3. Liberty Mutual
Direct Premiums Written: $33.8 billion
Market Share: 5.3%

4. Allstate
Direct Premiums Written: $31.5 billion
Market Share: 4.9%


5. Progressive
Direct Premiums Written: $27.8 billion
Market Share: 4.3%

6. Travelers 
Direct Premiums Written: $24.8 billion
Market Share: 3.9%

7. Chubb 
Direct Premiums Written: $21.2 billion
Market Share: 3.3%


8. USAA
Direct Premiums Written: $20.1 billion
Market Share: 3.1%

9. Farmers
Direct Premiums Written: $19.8 billion
Market Share: 3.1%

10. Nationwide
Direct Premiums Written: $19.2 billion
Market Share: 3.0%

Now we try to give some basic description about the above insurance company.

State Farm:

State Farm is a large group of insurance and financial services companies throughout the United States with corporate headquarters in Bloomington, Illinois. The group’s main business is State Farm Mutual Automobile Insurance Company, a mutual insurance firm that also owns the other State Farm companies. State Farm is ranked No. 36 on the 2018 Fortune 500 list of the largest United States corporations by total revenue.
(Source – wiki)

Berkshire Hathaway:

Berkshire Hathaway Inc. is an American multinational conglomerate holding company headquartered in Omaha, Nebraska, United States. The company wholly owns GEICO, Duracell, Dairy Queen, BNSF, Lubrizol, Fruit of the Loom, Helzberg Diamonds, Long & Foster, Flight Safety International, Pampered Chef, and NetJets, and also owns 38.6% of Pilot Flying J; 26.7% of the Kraft Heinz Company, and significant minority holdings in American Express (17.6%), Wells Fargo (9.9%), The Coca-Cola Company (9.4%), Bank of America (6.8%), and Apple (5.22%). Since 2016, the company has acquired large holdings in the major US airline carriers, and is currently the largest shareholder in United Airlines and Delta Air Lines, and a top three shareholder in Southwest Airlines and American Airlines.[5] Berkshire Hathaway has averaged an annual growth in book value of 19.0% to its shareholders since 1965 (compared to 9.7% from the S&P 500 with dividends included for the same period), while employing large amounts of capital, and minimal debt.(Source – Wiki)

 Liberty Mutual:

Liberty Mutual Group, is an American diversified global insurer, and the third-largest property and casualty insurer in the United States. It ranks 68th on the Fortune 100 list of largest corporations in the United States based on 2017 revenue. Based in Boston, Massachusetts, it employs over 50,000 people in more than 900 locations throughout the world. As of December 31, 2016, Liberty Mutual Insurance had $121.7 billion in consolidated assets, $102.5 billion in consolidated liabilities, and $38.3 billion in annual consolidated revenue. The company, founded in 1912, offers a wide range of insurance products and services, including personal automobile, homeowners, workers’ compensation, commercial multiple peril, commercial automobile, general liability, global specialty, group disability, fire and surety. (Source -Wiki)

Allstate:

The Allstate Corporation is one of the largest insurance providers in the United States and one of the largest that is publicly held. The company also has personal lines insurance operations in Canada. Allstate was founded in 1931 as part of Sears, Roebuck and Co., and was spun off in 1993. The company has had its headquarters in Northfield Township, Illinois, near Northbrook since 1967. Allstate ranked No. 79 in the 2018 Fortune 500 list of the largest United States corporations by total revenue. Its current advertising campaign, in use since 2004, asks, “Are you in good hands?” (Source – Wiki)

Progressive:

The Progressive Corporation is an American insurance company. It is one of the largest providers of car insurance in America. The company insures motorcycles, boats, RVs and commercial vehicles, and provides home insurance through select companies. Progressive has expanded internationally as well, offering car insurance in Australia. The company was co-founded in 1937 by Jack Green and Joseph M. Lewis, and is headquartered in Mayfield Village, Ohio.[1] Progressive is currently ranked No. 99 in the 2019 Fortune 500 list of the largest United States corporations by total revenue.(Source – Wiki)

Travelers:

The Travelers Companies, Inc., commonly known as Travelers, is an American insurance company. It is the second-largest writer of U.S. commercial property casualty insurance, and the third-largest writer of U.S. personal insurance through independent agents. Travelers is incorporated in Minnesota, with headquarters in New York City, and its largest office in Hartford, Connecticut. Travelers also maintains a large office in St. Paul, Minnesota. It has been a component of the Dow Jones Industrial Average since June 8, 2009.(Source – Wiki)

Chubb:

Chubb Limited, incorporated in Zurich, Switzerland, is the parent company of Chubb, a global provider of insurance products covering property and casualty, accident and health, reinsurance, and life insurance. Chubb operates in 54 countries and territories and in the Lloyd’s insurance market in London and is the world’s largest publicly traded property and casualty insurer. Clients of Chubb consist of multinational corporations and local businesses, individuals, and insurers seeking reinsurance coverage. Chubb provides commercial and personal property and casualty insurance, personal accident and supplemental health insurance, reinsurance and life insurance. The current company arose when ACE Limited acquired Chubb in 2016, then adopted the Chubb name.(Source – Wiki)

USAA:

The United Services Automobile Association (USAA) is a San Antonio, Texas-based Fortune 500 diversified financial services group of companies including a Texas Department of Insurance-regulated reciprocal inter-insurance exchange and subsidiaries offering banking, investing, and insurance to people and families who serve, or served, in the United States military. At the end of 2017, there were 12.4 million members.(Source – Wiki)

 Farmers:

Farmers Insurance Group (informally Farmers) is an American insurer group of automobiles, homes and small businesses and also provides other insurance and financial services products. Farmers Insurance has more than 48,000 exclusive and independent agents and approximately 21,000 employees. It is a subsidiary of the Swiss company Zurich Insurance Group. (Source – Wiki)

Nationwide:

Nationwide Mutual Insurance Company and affiliated companies is a group of large U.S.insurance and financial services companies based in Columbus, OH. The company also operates regional headquarters in Des Moines, IA; San Antonio, TX; Gainesville, FL; Raleigh, NC; Sacramento, CA, and Westerville, OH. Nationwide currently has approximately 34,000 employees, and is ranked #73 in the 2019 Fortune 500 list. Nationwide is currently ranked #53 in Fortune’s “100 Best Companies to Work For”. (Source – Wiki)