People make the mistake of equating size with profits.
Most successful corporations make about 10% profit, which hold for the small as well as the large.
Some of the new digital corporations and the hardware companies making digital equipment make much more than 10%(Apple, Facebook, etc.), but that doesn't hold for corporations as a whole.

Insurance companies are an integral part of the American financial system. Their money is invested in businesses of all kinds and physical property. In other words, part of their function is that of other financial institutions.

I am a small shareholder in, and take life insurance from, Massachusetts Mutual, one of the largest.
(Customer of long-standing, the dividends they pay me on my insurance exceed the premiums I pay them.

Revenue in 2011-25 billion
Assets managed- c. 450 billion
Insurance in force- c. 500 billion
Policyholders reserves- 74 billion
Paid to shareholders- 1.3 billion
Assets- 148 billion
Liabilities (inc. mandated reserves, taxes, dividends, etc.- 137 billion
Surplus- 11 billion

My health insurance is with another company, but that is part of my employment-retirement setup. It covers everything not paid by my Provincial health insurance (dental, drugs, physio, , equipment such as walkers and wheelchairs, specialists charges, etc. The province only pays part of these expenses).