I have a defined benefits pension plan, although my company does not offer it to new hires. By law, a pension must be funded in an “actuarially sound manner”. Basically, that means the assets in the fund must cover something like 80% of expected future claims. This goes back to the Rheingold Brewery closure in the 1970’s, when employees were left out in the cold. The resulting Javits Law required private (but not public!) pensions to actuarially sound.
Government pensions, unfortunately, are held to a lower standard of required funding.