Microsoft (Nasdaq: MSFT) is one of three U.S. companies with a AAA rating by S&P following ADP's (NYSE: ADP) decision to separate the Dealer Services business into an independent publicly traded company through a tax-free spin-off of 100% of Dealer Services to ADP shareholders.

The other two U.S. companies include Johnson & Johnson (NYSE: JNJ) and Exxon Mobil (NYSE: XOM).

You can read more on the S&P downgrade here.

S&P had 60 U.S. companies at AAA back in 1980 and that number fell to six in 2008. Dropping off over the last few years include General Electric (NYSE: GE), Pfizer (NYSE: PFE), and, now, ADP.

Shares of Microsoft are lower in early trading.