The funded levels of General Motors Co.'s U.S. pension plans improved significantly in 2010, aided by strong investment returns and a $4 billion cash contribution. At year-end 2010, the plans were underfunded by $11.5 billion, a sharp improvement from year-end 2009, when the plans had $16.2 billion in unfunded liabilities, GM disclosed Feb. 24 in reporting its fourth quarter and 2010 financial results. In addition, the plans were 89 percent funded at end of last year, up from 84 percent a year earlier. The results exclude $2 billion in company stock that GM contributed to the plans last month. Filed by Jerry Geisel of Business Insurance, a sister publication of Workforce Management. To comment, e-mail email@example.com. Stay informed and connected. Get human resources news and HR features via Workforce Management's Twitter feed or RSS feeds for mobile devices and news readers.