The funded status of the 100 largest corporate defined benefit pension plans dropped by $67 billion during January, as measured by the Milliman 100 Pension Funding Index. The deficit declined to $140 billion from $73 billion at the end of December 2013, primarily due to a 28-basis-point drop in the benchmark corporate bond interest rates used to value pension liabilities. Pension assets also experienced a modest loss during January, contributing to the funded status deficit.