Analysis from Towers Watson last summer indicated sponsors of defined benefit pension plans could receive billions in temporary funding relief from the federal government. Under the Preservation of Access to Care for Medicare Beneficiaries and Pension Relief Act of 2010 (the Act), employers with underfunded DB plans may elect to amortize funding shortfalls for any two plan years between 2008 and 2011 either over a 15-year period or by making interest-only payments for two years followed by seven years of amortization. Generally, DB sponsors are required to amortize shortfalls over seven years.

[See related: Lawmakers join businesses to call for pension relief]

While the funded status for the year changed only modestly, the year was marked by several significant events, according to Milliman. In August, falling interest rates drove up the projected benefit obligation and resulted in a record deficit for the 11 year history of this study. Over the course of the year, several companies adopted new accounting approaches, which involved full or substantive recognition of accumulated losses and a larger charge to 2010 balance sheets. Had similar accounting changes been instituted across all of the companies in this study, the resultant charge would have totaled $342 billion.

Despite the eventful (and sometimes volatile) year, pension investment strategies remained relatively consistent.

"For the year, the asset allocation of these 100 pension plans did not change significantly, as investment in equities only decreased from 45 percent to 44 percent," said Paul Morgan, co-author of the Milliman Pension Funding Study. "Fixed income allocations were unchanged at 36 percent, but allocations to other (alternative) investments increased from 19 percent to 20 percent. On average, there were not many changes, though we did see eight of the 100 companies decrease their equity allocations by more than 10 percent."