Here are several helpful breakdowns by Investopedia by Insurance industry category.

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) $21.1 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)

Property & Casualty

Company Net Premiums Written
State Farm Group $50.8 billion
Allstate Insurance Group (ALL) $24.8 billion
Liberty Mutual $21.5 billion
Berkshire Hathaway (includes GEICO) $21.4 billion
Travelers Group (TRV) $20.6 billion
American International Group (AIG) $19.7 billion
Nationwide Group $14.5 billion
Progressive Insurance Group (PGR) $14.5 billion
Farmers Insurance Group $14.1 billion
USAA Group $10.7 billion

(Source A.M. Best)

Life Insurance Companies

Company Total Direct Premium Market Share
MetLife (MET) $11.5 billion 7.98%
Northwestern Mutual $9.4 billion 6.55%
Prudential of America (PRU) $8.4 billion 5.79%
New York Life $7.8 billion 5.42%
Lincoln National $6.1 billion 4.27%
MassMutual $5.1 billion 3.52%
John Hancock $4.8 billion 3.37%
Aegon (AEG) $4.1 billion 2.82%
State Farm $4.0 billion 2.79%
Guardian Life Insurance Co. $3.4 billion 2.34%

(Source: NAIC)

 

Health Insurance Companies

Company Total Direct Premium Market Share
United Healthcare (UNH) $66.8 billion 11.70%
Wellpoint Group (WLP) $55.7 billion 9.75%
Kaiser Permanente $43.7 billion 7.66%
Humana (HUM) $21.7 billion 3.81%
Aetna (AET) $21.7 billion 3.81%
Health Care Service Corp $14.9 billion 2.60%
American Family $11.6 billion 2.04%
Highmark $11.4 billion 2.01%
Blue Cross/Blue Shield $9.8 billion 1.72%
Cigna (CI) $9.6 billion 1.69%

(Source: NAIC. Caveat emptor: The sales data on health insurance companies is from 2007, the last year of available data. The Affordable Care Act (aka ‘Obamacare’) may have altered these standings.)


 

Source: Top 10 Insurance Companies By The Metrics