Did you by any chance already have a separate TD Ameritrade account? The original TD Ameritrade account had to be linked with your Scottrade to avoid ending up with two separate accounts. You use your original Scottrade login to access the new TD Ameritrade account. TD Ameritrade does not require a minimum balance to maintain an account. My original has had a measly $40 balance in it for the last five years. USAA will liquidate your account if you fall below $500.