40 ILCS 5/11-205
Amounts contributed by the city for prior service annuity, widow's prior service annuity and minimum annuities, shall be credited to this reserve.
Prior service and widow's prior service annuities payable under this Article and that part of any minimum annuity which is in excess of the age and service and prior service annuity shall be charged to this reserve.
If the balance of the investment and interest reserve is not sufficient to permit a transfer from that reserve to the annuity payment reserve to make the credit balance of the annuity payment reserve equal to the liabilities chargeable thereto (including the present values of all annuities entered upon or fixed and of all annuities not entered upon), amounts necessary for such purpose shall be transferred from this reserve to the investment and interest reserve.
40 ILCS 5/11-205