215 ILCS 5/173.4
Such reinsurance agreement may provide that the liquidator or receiver of an insolvent ceding company shall give written notice of the pendency of a claim against the insolvent ceding company on the policy or bond reinsured within a reasonable time after such claim is filed in the insolvency proceeding and that during the pendency of such claim any assuming company may investigate such claim and interpose, at its own expense, in the proceeding where such claim is to be adjudicated any defense or defenses which it considers available to the ceding company or its liquidator or receiver. The expense thus incurred by the assuming company is chargeable against the insolvent ceding company as a part of the expense of liquidation to the extent of a proportionate share of the benefit which accrues to the ceding company solely as a result of the defense undertaken by the assuming company.
Where two or more assuming companies are involved in the same claim and a majority in interest elect to interpose a defense to such claim, the expense shall be apportioned in accordance with the terms of the reinsurance agreement as though such expense had been incurred by the ceding company.
215 ILCS 5/173.4