Rating agency Standard & Poor’s has awarded billionaire investor Warren Buffett’s new municipal bond insurance company a triple-A rating, the same top-level ranking some rival insurers have been downgraded from in recent months amid the credit market turmoil.

S&P last week said Berkshire Hathaway Assurance Corporation, which has been granted licences to operate in by 48 US states and the District of Columbia, will obtain its highest ranking due to its large capital reserves and guarantee from an insurer owned by Buffett.