[Praxeologue]

Your link notes that the Pension Benefit Guaranty Corporation does not insure state, county or local plans, i.e. Detroit.

[uncommonsense]

There are 2 types of plans - single and multiemployer plans. The multiemployer plans cover all sorts of unions:

"Under Title IV of the Employee Retirement Income Security Act of 1974 (ERISA), the Pension Benefit Guaranty Corporation (PBGC) administers two very different pension insurance programs—one covers single-employer plans and the other covers multiemployer plans. These programs are separately funded and maintained."

Check out their data books to see how union companies and national unions have tanked the security of their workers: Pension Insurance Data Books