Search for the company (by ticker symbol or company name).
On the Company Details tab, click on Long Term Debt. Select a bond from the listing to get the ratings (Fitch, Moody's & S&P Rating) on the "Issue Details".
Factset provides credit ratings [It is available in the Trading Room ]
Launch Factset
Click on Company/Security Tab
Look up a company i.e. GE
In the "Reports" frame on the left, expand Credit Analyses and click on DCS Overview to view the current credit ratings from Moody's S& P & Fitch.
More information about Moody's Ratings, and how they are calculated, is available from Moodys.