According the USA TODAY (see here):
The nation’s largest health insurer warned Thursday that it may pull out of the Obamacare exchanges after 2016 – forcing more than a half million people to find other coverage – after low enrollment and high usage cost the company millions of dollars.
The possible move by UnitedHealth Group raises new questions about the viability of President Obama’s signature health law and follows the departure of more than half of the non-profit insurance cooperatives this year. If UnitedHealth drops out, consumers would lose one of the lowest-cost plans available in much of the country, and some wonder how smaller insurers could fill the void.
UnitedHealth warned investors that it would reap $425 million less in revenue during the fourth quarter than it had previously expected.