The selloff came as more than $2.7 trillion worth of options expired, an event which typically spurs heightened volatility.

U.S. stocks fell Friday on word of a government investigation into UnitedHealth (UNH) and gloomy economic updates, driving Wall Street's major averages toward losses for the week. The S&P 500 (SP500) was -0.

UnitedHealth Group stock is sinking Friday on reports the Justice Department is investigating the health insurer. Here's what to know.

UnitedHealth Group shares tumbled Friday on a report that the U.S. Department of Justice has started an investigation into the health care giant's Medicare billing practices.

The Justice Department is probing diagnoses and practices that triggered extra payments to UnitedHealth’s Medicare Advantage plans, people familiar with the matter say.