Those ratings that castigate Afghanistan and some other poor countries as hopelessly “corrupt” always imply that the United States is not corrupt.
While it is true that you don’t typically have to bribe your postman to deliver the mail in the US, in many key ways America’s political and financial practices make it in absolute terms far more corrupt than the usual global South suspects. After all, the US economy is worth over $16 trillion a year, so in our corruption a lot more money changes hands.