Moody's lowers Berkshire Hathaway rating

Warren Buffett's Berkshire Hathaway Inc. (BRKA) took another blow from a rating company, this time from Moody's Corp., a big Berkshire holding. Moody's on Wednesday lowered the long-term issuer rating of Berkshire to Aa2 from its top Aaa rating. It cited the weakening economy and "severe decline in equity markets."

Berkshire has had big losses in its portfolio, which includes large financial companies such as Wells Fargo & Co. and American Express Co. Buffett is weathering one of the toughest markets since he took over Berkshire in 1965. Its shares are down 33 percent over the past year. Further downgrades could impact borrowing costs, and hurt its ability to charge maximum rates for insurance policies written by its subsidiaries.

Last month, Fitch Ratings stripped Berkshire of its AAA, citing concerns about its stock holdings and exposure to several long-term derivatives contracts written in recent years. In late March, S&P revised its rating outlook for Berkshire to "negative" from "stable" due in part to concerns about its equity holdings. But it retained its AAA rating on Berkshire.