Quote from LeeD:
I understand TOS means ThinkOrSwim. They must offer a decent rate on the positive account balance. It's likely to be better than what any bank offers on 1-year deposits.
they must?
here is IB rates-
http://www.interactivebrokers.com/en/accounts/fees/interest.php
TOS-
https://www.thinkorswim.com/tos/myAccounts/displayRates.tos