Illinois' biggest public pension fund, the Teachers' Retirement System, reported Tuesday that it posted an 18 percent return on investments in fiscal 2014, far surpassing its assumed annual rate of 8 percent.

The TRS said that its assets as of June 30 totaled $45.3 billion, up 14.9 percent from the end of fiscal year 2013.

Dick Ingram, the fund's executive director, said that despite the good investment news, the retirement system will continue to stress to its members, state officials and the public that "TRS cannot invest its way out of the current underfunded liability created by decades of state funding shortfalls."

Illinois has a $100 billion unfunded liability for its five state retirement systems, including TRS, and the lowest funded rate among all the states.

The state is currently defending the constitutionality of a pension reform law enacted in December that is aimed at shrinking the liability by reducing and suspending cost-of-living increases for pensions, raising retirement ages and limiting the salaries on which pensions are based.

A coalition of labor unions and other parties challenging the law have asked a state court judge for an expedited ruling in their favor.