benefits in the future, that is accounted for as a liability. State and Local Governments were required to do the same thing in the mid-2000s (Governmental Accounting Standards Board (GASB)).
The Post Office should do the same.
In any event, I don't see it as a terrible requirement for the USPS to release pricing data to receive a $10 B loan that gets them at least through the year. That requirement seems mostly symbolic since trump could pick up the phone, call his recent Postmaster appointee and say send it to me. In fact, I bet the feds already have it.
Info on GASB rules on Local and State Government accounting for retiree benefits:
https://www.cbpp.org/research/accounting-for-the-cost-of-retiree-health-and-other-benefits-gasb-45