General Motors Corp., Detroit, reduced its pension obligations by $3.9 billion after it re-measured its U.S. salary and hourly pension plans, according to a filing with the SEC today. The automotive company's pension obligations now stand at $85 billion, compared with roughly $89 billion at the end of last year. GM re-measured the plans after roughly 34,400 hourly employees accepted early retirement packages or buyouts as part of an attrition plan earlier this year, said spokeswoman Brenda Rios. The decrease was also based on a reduction in the overall pension benefits GM implemented in February and a change in the company's discount rate. It now uses a weighted average discount rate of 6.15% to determine its benefit obligations, compared with the 5.7% at year-end 2005, according to the filing.