If you have more in an IB account than the FDIC will cover (100,000 USD) but you don't want to invest all of it in stocks to get full SPIC protection, what low risk security would you recommend, so that an account is technically fully insured?
FDIC insurance only applies to banks and isn't applicable to monies kept at a broker dealer. SIPC insurance covers up to $500k in assets and $100k in cash, however, it doesn't protect funds deposited solely for the purpose of earning interest. According to the FINRA website, SIPC protection covers notes, stocks, bonds, mutual funds, and registered securities. So I would guess that the safest place to put your money would be in Treasury Notes, that way you would be backed by the full faith and credit of the government as well as the SIPC.