Why are the assets in a pension plan not reported on the balance sheet of the entity

Question:

Why are the assets in a pension plan not reported on the of the entity sponsoring the pension plan? Does this treatment result in an understatement of the sponsoring entity's assets?

Balance Sheet
Balance sheet is a statement of the financial position of a business that list all the assets, liabilities, and owner’s equity and shareholder’s equity at a particular point of time. A balance sheet is also called as a “statement of financial...