I looked at Schwab, Fidelity, eTrade, Vanguard, TD Ameritrade and Robinhood to compare the options available for uninvested cash. Some offer no automatic options to invest the idle cash or earn any interest on it. Schwab is one such example that requires the user to purchase money market mutual funds or other products to invest the idle cash. Etrade and Ameritrade also do the same but Etrade does have a savings account now.
Vanguard and Fidelity have options to auto invest the uninvested cash in a money market account.
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