> Yes, but it has an exception for treason and felonies
There are two separate parts:
1. While they are attending a session they can't be arrested, and
2. They can't be held accountable in any other forum based on the content of any speech or debate in either House.
The exception for for treason, felonies, and "breach of peace" applies to the first; the second, is an absolute, unqualified immunity, and, as applied by the Supreme Court, applies to all "legislative acts", which includes quite a bit that is not physically on the floor during a general session of the House.
As numerous commentators have pointed out, treason is a ridiculously high standard that has rarely been met. It has been misapplied so often by politicians using hyperbole that most people don't understand the meaning anymore.
It requires not just "aid and comfort" to the enemy, but also "adherence to the enemy" actively waging war against the United States, according to Supreme Court precedent. You cannot accidentally commit treason.
