我問過Fidelity, 他們告訴我

雖然不是FDIC 保險，但是有SIPC covered. 

If Fidelity were to collapse, the Securities Investor Protection Corporation (SIPC) would protect customer assets. SIPC coverage includes up to $500,000 in securities, with a $250,000 limit for cash, and would help transfer accounts to another brokerage or oversee liquidation. While individual investment losses due to market fluctuations are not covered, SIPC ensures the safety of assets held within Fidelity's brokerage accounts.