One large health insurer is going to draw on services from another large health insurer to help its biggest customers.

Principal Financial Group Inc., Des Moines, Iowa, says it has agreed to offer employer customers with self-funded health plans access to Aetna Signature Administrators services from Aetna Inc., Hartford.

The agreement will permit the employer customers to use Aetna’s national preferred provider network and stop-loss insurance program, Principal says.