Fannie Mae and Freddie Mac may currently have a higher credit rating from S&P and Fitch than Uncle Suggy. Mark Zandi's Moodys gives both a triple AAA, I believe.
I think Warren Buffett owns Moodys and as a good opportunist and Insurer against Natural Disasters Warren keeps over $100B in short term US T-Bills on Berkshire Hathaway's books. That may be why Moodys hasn't downgraded US Government Debt yet.