Illinois constitution prohibits default on public pensions. Taxpayers on the hook for shortfalls.
http://ww w.ilga.gov/commission/lrb/con13.htm
SECTION 5. PENSION AND RETIREMENT RIGHTS
Membership in any pension or retirement system of the
State, any unit of local government or school district, or
any agency or instrumentality thereof, shall be an
enforceable contractual relationship, the benefits of which
shall not be diminished or impaired.
(Source: Illinois Constitution.)