The dollar rallied on Wednesday ahead of the Federal Reserve's decision on interest rates, but retreated from the day's highs after markets stabilised from an early shock caused by the detention of Turkish President Tayyip Erdogan's main rival. Traders are also digesting the Bank of Japan's earlier decision to hold interest rates steady, while the Fed's policy decision later will be crucial for investors eager to know what the central bank makes of Trump's policies and their impact on the U.S. economy, and how that affects the rate outlook.