The U.S. dollar slid against other major currencies as markets awaited testimony from Federal Reserve Chair Janet Yellen. The dollar index measuring the greenback against six currencies was down 0.28%. Yellen will present the Fed's monetary policy report and investors will watch for clues about future interest rate increases. The chance of a rate hike in June is seen as just below 50%. The dollar also fell after President Trump's national security adviser Michael Flynn resigned amid allegations about discussing sanctions with Russia.