Not paying attention to your idle balances? You might be throwing away $500 a year. If you are like most bank and brokerage customers, you’re getting gouged on your cash holdings. For years, there was no need to shop around. The Federal Reserve held overnight interest rates close to zero. If all you got out of your short-term savings was no-fee checking, you were getting a pretty good deal. Now, with overnight yields above 2%, cash returns matter. If you’ve got $25,000 of idle cash between your checking and your brokerage account, and you don’t pay attention, you might get nicked out of $500 a year……………