The insurer of your funds depends on where they are invested. Within your Treasury account custodied at BNY Mellon Pershing, your funds enjoy a combination of $5.25M FDIC insurance on funds in the Dreyfus Bank Sweep and an additional $500K SIPC insurance on funds invested in Money Market Funds and/or Treasury Bills.
Money Market Funds have their assets invested in cash, U.S. government securities, and/or repurchase agreements collateralized by government securities. T-Bills are backed by the U.S. government.