I'm no expert on the nuts and bolts of the Illinois pension fund, but public pensions have been under attack by Wall Street for many years. Current Ohio Governor John Kasich was a Lehman Brothers goon back in the early and mid-2000s, under Bob Taft. He lobbied endlessly to have Ohio's public pensions taken over by Lehman, which of course went bankrupt in late 2008, because Dick Fuld was the smartest guy in the room.
Also during the reign of Taft, the republican legislature changed management of the public funds to permit new types of investing. That led to the absolutely hysterical Coingate scandal. A buddy of Taft invested pension funds in rare coins, and tens of millions mysteriously disappeared.
https://en.wikipedia.org/wiki/Coingate_scandal
FFWD to the 2010s, and most pension funds are still invested primarily in bonds and blue chip stocks. This period of unprecedented low interest rates has undermined the funds as well as limited hiring during the recession. Some funds also have real estate investments, which generally are doing well, but bonds remain the backbone of most funds, as they should be.