求翻译：国际信用评级机构标准普尔标普于美国东部时间5日晚间表示，公司已经将美国的主权信用评级由原来的最高级AAA下调至AA+。这在历史上尚属首次。是什么意思？

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International credit rating agency Standard and Poor's in the United States Eastern Standard Time on the night of 5 will be the United States, said the company has been the sovereign credit rating from the original summit AAA downward to AA+. This is the first time in history.

International credit rating organization Standard & Poor's sign Pu on 5th in the evening indicated in the American Eastern Time that, the company US's sovereignty credit rating will already decline by original highest-level AAA to AA+.This still was in the history for the first time.

International credit rating agency standard and poor's p in United States Eastern time 5th said late, the company has United States sovereign credit ratings from the highest level of AAA downgraded to AA +. This is the first time in history.