Firms carry errors and omissions insurance in case they mess up and are sued. Other than that SIPC insurance is provided to all investors. Here's a blurb from the SIPC website...
What SIPC Covers... What it Does Not
The cash and securities such as stocks and bonds held by a customer at a financially troubled brokerage firm are protected by SIPC.
Among the investments that are ineligible
for SIPC protection are commodity futures contracts (unless defined as customer property under the Securities Investor Protection Act) and currency, as well as investment contracts (such as limited partnerships) and fixed annuity contracts that are not registered with the U.S. Securities and Exchange Commission under the Securities Act of 1933.
It is important to recognize that SIPC does not work the same way as the Federal Deposit Insurance Corporation in terms of blanket protection of losses. For more information click here