CS was primarily funded by members in the transportation industry, deregulation came along in the 80's, some organized companies merged and others folded and closed doors. Fewer employees making contributions to cover the vast number of retirees collecting caused a significant imbalance. It became insolvent and needed a bailout, benefits haven't increased.
Western is extremely diversified, remaining completely funded and solvent.
I don't know about other regions and cannot speak to their contributions or sustainability.
Maybe someone else can elaborate on those, hope this helps.