Regulators are investigating allegations that dealers colluded and manipulated key reference rates in the $5.3 trillion-a-day foreign currency market, which is the world’s biggest and least regulated. Bank of America revised its results to add $400 million to its legal reserves to cover expected settlements related to foreign exchange, adding it was in advanced discussions with U.S. The bank said in a filing it was being investigated by government authorities in North America, Europe and Asia but did not disclose which regulators it was in talks with.