In that case, they aren't liabilities either.
any more than the outstanding balance on a credit card is an asset.
Your example is money already spent and that's a liability. That's different than money promised to be spent.
OK, how about if we say “The Social Security program has promised to pay $126 trillion more than it has forecast revenue”?
Though, since there’s no forecast end-date to Social Security, and it’s expenses are starting to exceed revenue, its promises-to-pay in excess of its anticipated revenue are actually infinite.