Please explain....”pension funds that are not separate from the corporation”
DEC’s pension funds (now HP or whomever is the current iteration of DEC) are in a separate retirement fund entity. They have no financial ties to HP or any other public corporation. HP’s bankruptcy would not effect retirees’ pensions.
If I understand correctly, GM and subsidiaries negotiated retirement benefits intending to pay them out of future profits. That meant they created future liabilities without funding them. Union retirees are essentially sitting on a pile of bad debt that won't be repaid.