It should say it on the packaging...something like 12% or 14% solution added. To me it is not the same thing as brining. I am not against the injection, as it usually has seasonings along with the sodium solution and sodium phosphate, which is good for moisture retention and transmutation of the seasoning through out the meat. It is a way for the producers to get more weight on their birds fo less price, so I get that too!
I have not cooked a Butterball in about 5 years, but when we did have them, I always brined.