Miami ? Cigna Corp. has agreed to spend more than $500 million to settle a lawsuit claiming the insurer routinely shortchanged doctors on payments for their services, sources close to the talks said Wednesday.

The proposed settlement would require Cigna to pay at least $140 million, but that amount was expected to rise to about $170 million, according to the sources. That includes a minimum of $70 million to reimburse claims up to 12 years old, along with money to start a foundation and pay legal costs.

The nation’s third-largest health insurer also committed to spending $400 million to change its claims processing procedures, the source said. Most of that money has been spent in the last two years.

The agreement, to be presented today in federal court in Miami, follows a $470 million settlement reached with Aetna in May and leaves eight other insurers as defendants in the class-action lawsuit.