Excerpt: According to new congressional estimates, the government-run insurer of traditional pensions could face a bill of more than $120 billion over the next decade to cover pension fund losses, BusinessWeek has learned. That far exceeds the $23 billion that the PBGC estimates it needs to pay off workers and retirees. The PBGC's liabilities include the $6.6 billion in unfunded United Airlines (UAL ) pension obligations that the agency absorbed on May 10.