WSJ:

(The) Pension Benefit Guaranty Corp's ... previous estimate for these companies' so-called level of underfunding was $35 billion. Overall, the agency says, all private employer pension plans are $400 billion short of assets needed to keep promises they've made....

..."In the worst case, PBGC's deficit could grow so large that the size of the premium increase necessary to close the gap would be unacceptable" to healthy companies, Mr. Kandarian (of the Pension Benefit Guaranty Corp) said. "If this were to occur, Congress could call upon U.S. taxpayers to pick up the cost of underfunded pension plans through a federal bailout."