Berkshire Hathaway Assurance Corp., Columbia Insurance Co., General Reinsurance Corp. and Government Employees Insurance Company (GEICO) were other insurance companies affected by the downgrade.

In his annual letter to investors from late February, Buffett acknowledged Berkshire's $7.5 billion investment and derivative losses, but said the U.S. still had its best days ahead of it.

"Though the path has not been smooth, our economic system has worked extraordinarily well over time," Buffett wrote. "It has unleashed human potential as no other system has, and it will continue to do so.

Moody's said it could further downgrade Berkshire if it took on more risk, experienced continued losses in insurance underwriting, investments or derivatives that cause a 20% in shareholder equity or a "material decline" in operating cash flow.
Gannon joined TheStreet.com in March 2007, after spending more than six years as a reporter and editor for The Journal News in Westchester County, N.Y., most recently as an assistant metro editor. He earlier covered several political and government beats as a reporter, including the city of Yonkers. Earlier in his career, he covered venture capital, private equity and the IPO market for Thomson Financial�s Venture Capital Journal and advertising for Sales-Fax, a small, independent trade weekly. He earned a B.A. in history from the College of the Holy Cross and an M.S. in journalism from Northwestern University�s Medill School.

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