Trinity Health, the Michigan-based owner of Saint Alphonsus Health System in the Treasure Valley, has signed a preliminary agreement with Pennsylvania-based Catholic Health East to merge into a unified national health system.

The nonbinding letter of intent was announced Wednesday.

The consolidation would create a 21-state health system with 82 hospitals, 89 continuing-care facilities and home health and hospice programs. It would have more than 87,000 employees, including 4,100 employed physicians. Annual operating revenues are expected to be about $13.3 billion. The system would provide an estimated $1 billion of charity care and community programs per year.

"We are very pleased and excited about the benefits of coming together," said Sally Jeffcoat, president and CEO of Boise-based Saint Alphonsus. "By combining our systems into one, we further strengthen our ability to heal the body, mind and spirit of the people and communities we serve."

The merger would give providers more access to resources and would bring patients more coordinated and integrated care, officials said.

The systems said their boards and managers have a spring 2013 target date for a final agreement.