Capital losses offset capital gains, not interest and dividend income.
However, if you have a capital loss that is more than your capital gains, you can deduct $3000 of that loss against any other income (wages, interest, dividends, prizes, etc.). Any un-used loss will be carried over to next year, and used to offset any gains first. If there is still a loss carryover after zeroing out your gains, you can deduct another $3000 against other income, and the cycle continues.
