Health Care Service Corp. has completed its acquisition of third-party administrator Trustmark Health Benefits, the companies announced Wednesday.

Health Benefits is now a wholly owned subsidiary of HCSC, which sells Blue Cross Blue Shield plans to 17 million members in Illinois, Montana, New Mexico, Oklahoma and Texas. The subsidiary previously operated under employee benefits vendor Trustmark.

The acquisition will boost HCSC’s offerings to self-insured customers, the company said in a news release.

“It is the latest way we’re developing and building out our network of subsidiaries and investments in businesses with interests affiliated with ours — as we seek to increase access to quality, cost-effective health care,” Dr. Opella Ernest, executive vice president of commercial markets for HCSC, said in the news release.

The not-for-profit insurer and benefits administrator announced the deal in August for an undisclosed price. Before the transaction, HCSC was a Trustmark customer and used its services to manage self-funded employers’ health spending.