29 C.F.R. § 4041A.41
General rule.
CFR 2016 annual edition (revised as of 2016-07-01) · current text
If a plan's assets, excluding any claim of the plan for unpaid withdrawal liability, are sufficient to satisfy all obligations for nonforfeitable benefits provided under the plan, the plan sponsor may close out the plan in accordance with this subpart by distributing plan assets in full satisfaction of all nonforfeitable benefits under the plan.