Federal prosecutors charged 15 people across multiple states in connection with an alleged Medicare and insurance fraud schemes they allege collectively took in $2 billion, the Justice Department said on Thursday.

Eight of the defendants, some of whom were physicians, were arrested by federal agents on Thursday, with most of the arrests taking place in California, according to officials.

The alleged schemes included billing private insurers for phony substance abuse treatment, billing Medicare for unnecessary atherectomy procedures (which are for removing plaque from blood vessels) and another charging Medicare for hospice services for patients who weren't terminally ill, the Justice Department said.