220 ILCS 5/16-111.3
At such time as the Board of Governors of the Federal Reserve System ceases to include the monthly average yields of 30-year U.S. Treasury bonds in its weekly H.15 Statistical Release or successor publication, the Monthly Treasury Long-Term Average Rates (25 years and above) published by the Board of Governors of the Federal Reserve System in its weekly H.15 Statistical Release or successor publication shall instead be used to establish a rate for the purpose of calculating the Index defined in subsection (e) of Section 16-111 of this Act, and at such time, such Monthly Treasury Long-Term Average Rates (25 years and above) shall also be used in place of the monthly average yields of 30-year U.S. Treasury bonds in the rate of return calculation required by subsection (d) of Section 16-111. An electric utility shall also remove the effects, if any, of any impairment due to the application of Statement of Financial Accounting Standards No. 142, which was issued in June 2001, when making the calculations required by this Section or by subsections (d) and (e) of Section 16-111.
220 ILCS 5/16-111.3