The Justice Department has reportedly launched an antitrust investigation into UnitedHealth, the nation’s largest health insurer and a top manager of pharmacy benefits and physician groups. Investigators have been digging into the relationship between the company’s insurance unit, which covers roughly 50 million people, and its Optum health services unit, which employs about 90,000 doctors, The Wall Street Journal reports. “Investigators have asked whether UnitedHealthcare favored Optum-owned gr