We are talking about insurance for defined benefit plans. The idea is to avoid a situation where workers and retirees end up with a much smaller pension when a company goes bankrupt. One example would be the people working for AbitibiBowater. That company has placed itself under the protection of the Companies' Creditors Arrangements Act. The capitalization of the pension plan is between 65% and 70%. If the company fails, the retirees and employees who contributed will no longer have a pension plan. They will be entitled to 65% of the value of their vested pension benefits.
On April 22nd, 2010. See this statement in context.