Recall that pension plan assets refer to the funds (e.g., cash and investments) set aside by the employer to pay retirement income to its employees in the future. 

Plan assets are NOT reported separately in a company's financial statements. Instead, plan assets are added together with the projected benefit obligation (PBO) and reported as either a net pension asset (if plan assets are > the projected benefit obligation) or a net pension liability (if plan assets are < the projected benefit obligation).

A trustee is a person who accepts employer contributions, invests the contributions, accumulates the earnings on the investments, and pays benefits from the plan assets to retired employees or their beneficiaries.

Expected return on plan assets is the estimated long-term return on invested assets.