The news: The Justice Department is investigating UnitedHealth Group’s billing practices, according to a WSJ report. The civil fraud investigation will assess whether UnitedHealth made up diagnoses for Medicare Advantage (MA) patients in order to get higher payments from the federal government. Shares of UnitedHealth Group fell ~10% on the heels of Friday’s WSJ report.

For context, health insurers operating MA plans get paid more by the government when they care for patients who are sicker and have certain diagnoses.

• More than half of Medicare members now get their benefits through MA.
• UnitedHealth is the largest MA provider, with about 29% market share, per KFF.