Banks provide various types of loans to customers. Short-term loans are usually provided against a customer's general credit standing or with collateral and are often for working capital needs. Medium and long-term loans typically require collateral. The Federal Reserve aims to stimulate the economy through lowering interest rates, buying mortgage and other assets, and committing to maintain low rates for a prolonged period. Quantitative easing can still impact the economy when rates are near zero through portfolio substitutions, altered policy expectations, and expansionary fiscal policy.