Pension plan funding levels among large publicly held U.S. employers improved slightly in 2009 due to strong investment returns, according to a survey released last week.

Defined benefit plans offered by 100 U.S. employers with the largest pension programs were, on average, 81.7% funded in 2009, up from 79.4% in 2008, according to the Milliman Inc. survey.

That improvement was the result of solid investment gains, according to the survey. On average, plans earned 14.1% on assets, a huge turnaround from 2008 when investment losses averaged 18.9%.

The turnaround would have been even bigger except for falling discount rates used to measure plan liabilities, according to the survey. A fall in discount rates inflates the value of plan liabilities for reporting purposes.

The market value of plan assets increased about $112 billion to nearly $1.09 trillion in 2009. On the other hand, the value of plan obligations increased by just more than $100 billion to $1.33 trillion, Milliman said.

Even with the improvement in funded status, plans' funded ratio in 2009 was the second-lowest since the actuarial consulting firm began the surveys in 1999 (see box).

Among surveyed employers, Detroit-based General Motors Co. had the biggest defined benefit program as measured by assets. Last year, GM had $98.5 billion in plan assets and its plans were 78.2% funded, down slightly from 78.4% in 2008. The $27.4 billion difference between its 2009 plan assets and $125.9 billion in benefit liabilities was by far the greatest of any of the 100 employers in the study.

With $98.5 billion in plan assets, Armonk, N.Y.-based IBM Corp. had the second-largest pension program in 2009. Its plans were 91% funded last year, up from 85.4% in 2008, according to the survey.

FPL Group Inc., a Juno, Fla.-based energy and utility company, had the highest funded ratio in 2009 at 162.3%, up from 156% in 2008.

Atlanta-based Delta Air Lines Inc. had the lowest funded ratio: 44.8%, down from 45.8% in 2008.

Seattle-based Milliman analyzed financial reports of publicly held companies sponsoring the 100 largest pension programs for which full-year data was available.

A summary of the survey, “Milliman 2010 Pension Funding Study,” is available at www.milliman.com.