Let's say USPS has promised to pay for a 20-year-old employee's health care for the next 70 years. Let's say the total price of that health care is going to be

Let's say USPS has promised to pay for a 20-year-old employee's health care for the next 70 years. Let's say the total price of that health care is going to be $10M over the 70-year course. What should they do that neither involves setting sufficient money aside today nor a significant chance of failing to fulfill their obligation? Keep in mind that USPS' core business can't turn much of a profit due to Congressionally-defined price caps, so it is a very poor place to "invest" money.