NextEra Energy's $5.4 billion retirement plan for employees has suffered about half a billion dollars in losses this year as outsized bets on company stock soured, reflecting ongoing risks of corporate 401(k) policies that encourage concentrated positions in company shares. America’s largest renewable power company is among several U.S. energy and utility companies, including Exxon and Southern Company, that continue to promote big, concentrated bets on company stock in worker retirement plans. A Reuters analysis of retirement policies and stock performance data, along with inter...