Sir Martin Sorrell, Chairman and Chief Executive Officer of WPP, the world's largest advertising company, speaks during an interview with Reuters at the Argentina Business and Investment Forum 2016 in Buenos Aires, Argentina, September 13, 2016. REUTERS/Marcos Brindicci

Sir Martin Sorrell, Chairman and Chief Executive Officer of WPP, the world's largest advertising company, speaks during an interview with Reuters at the Argentina Business and Investment Forum 2016 in Buenos Aires, Argentina, September 13, 2016. REUTERS/Marcos Brindicci

Sir Martin Sorrell, Chairman and Chief Executive Officer of WPP, the world's largest advertising company, speaks during an interview with Reuters at the Argentina Business and Investment Forum 2016 in Buenos Aires, Argentina, September 13, 2016. REUTERS/Marcos Brindicci

Sir Martin Sorrell, Chairman and Chief Executive Officer of WPP, the world's largest advertising company, speaks during an interview with Reuters at the Argentina Business and Investment Forum 2016 in Buenos Aires, Argentina, September 13, 2016. REUTERS/Marcos Brindicci

(FILES) This file photo taken on April 12, 2005 shows former head of insurer AIG Maurice Greenberg(C) being escorted through a subway tunnel as he leaves a meeting with New York Attorney General Eliot Spitzer in New York. New York's fraud case against Maurice "Hank" Greenberg, former chief executive of US insurance giant American International Group, finally began on September 13, 2016, 11 years after civil charges were first filed. Along with former chief financial officer Howard Smith, Greenberg, a legendary Wall Street figure, is accused by New York state's attorney general of deceiving investors by overseeing transactions that masked the company's true financial health and hid underwriting losses. Greenberg is now 91 and the case was brought in 2005 by former New York State Attorney General Eliot Spitzer, who later stepped down as New York governor in a 2008 prostitution scandal. / AFP PHOTO / DON EMMERTDON EMMERT/AFP/Getty Images

(FILES) This file photo taken on March 26, 2009 shows former chairman and CEO of American Insurance Group (AIG) Maurice Greenberg at a luncheon in Hong Kong. New York's fraud case against Maurice "Hank" Greenberg, former chief executive of US insurance giant American International Group, finally began on September 13, 2016, 11 years after civil charges were first filed. Along with former chief financial officer Howard Smith, Greenberg, a legendary Wall Street figure, is accused by New York state's attorney general of deceiving investors by overseeing transactions that masked the company's true financial health and hid underwriting losses. Greenberg is now 91 and the case was brought in 2005 by former New York State Attorney General Eliot Spitzer, who later stepped down as New York governor in a 2008 prostitution scandal. / AFP PHOTO / Mike CLARKEMIKE CLARKE/AFP/Getty Images

(FILES) This file photo taken on April 12, 2005 shows former head of insurer AIG Maurice Greenberg(L) leaving following a meeting with New York Attorney General Eliot Spitzer in New York. New York's fraud case against Maurice "Hank" Greenberg, former chief executive of US insurance giant American International Group, finally began on September 13, 2016, 11 years after civil charges were first filed. Along with former chief financial officer Howard Smith, Greenberg, a legendary Wall Street figure, is accused by New York state's attorney general of deceiving investors by overseeing transactions that masked the company's true financial health and hid underwriting losses. Greenberg is now 91 and the case was brought in 2005 by former New York State Attorney General Eliot Spitzer, who later stepped down as New York governor in a 2008 prostitution scandal. / AFP PHOTO / DON EMMERTDON EMMERT/AFP/Getty Images

NEW YORK, NY - SEPTEMBER 13: Traders and financial professionals work on the floor of the New York Stock Exchange (NYSE) ahead of the closing bell, September 13, 2016 in New York City. The Dow Jones industrial average fell 258 points on Tuesday. (Photo by Drew Angerer/Getty Images)