Buffett's biggest deal casts light on pension burden

Growing pension obligations at Precision Castparts Corp , which Berkshire Hathaway has agreed to buy for $32 billion, highlight an issue that large U.S. corporations still face, almost a decade into a low-interest rate environment. Berkshire's boss, Warren Buffett, has himself highlighted rising pension cost as an area of concern for the American economy. Back in 2007, Buffett said in a letter to shareholders that S&P 500 companies should not expect above-average returns on their pensio