Is *infallibilitas in credendo* a new or established doctrine within the Roman Catholic Church? In Pope Francis' recent interview, he says:


  Thinking with the church, therefore, is my way of being a part of this people. And all the faithful, considered as a whole, are infallible in matters of belief, and the people display this infallibilitas in credendo, this infallibility in believing, through a supernatural sense of the faith of all the people walking together. This is what I understand today as the ‘thinking with the church’ of which St. Ignatius speaks. When the dialogue among the people and the bishops and the pope goes down this road and is genuine, then it is assisted by the Holy Spirit. So this thinking with the church does not concern theologians only. ... This is how it is with Mary: If you want to know who she is, you ask theologians; if you want to know how to love her, you have to ask the people.


He even goes on to explain it a little bit, saying:


  and, of course, we must be very careful not to think that this infallibilitas of all the faithful I am talking about in the light of Vatican II is a form of populism. No; it is the experience of ‘holy mother the hierarchical church,’ as St. Ignatius called it, the church as the people of God, pastors and people together. The church is the totality of God’s people.


Thing is (and I almost hate to admit this), but I've never heard of that before.  "People Infallibility", if you will, seems rather novel. (And yes, I get that its not really that, but I can see it being misinterpreted as such).  Is this a new term, or one that I just missed out on being of from the heretic arm of the church? :)
This doctrine is taught in The Dogmatic Constitution of the Church of the Second Vatican Council, paragraph #12 as follows:


  "The holy people of God shares also in Christ's prophetic office; it spreads abroad a living witness to Him, especially by means of a life of faith and charity and by offering to God a sacrifice of praise, the tribute of lips which give praise to His name.(110) The entire body of the faithful, anointed as they are by the Holy One,(111) cannot err in matters of belief. They manifest this special property by means of the whole peoples' supernatural discernment in matters of faith when "from the Bishops down to the last of the lay faithful" (8*) they show universal agreement in matters of faith and morals. That discernment in matters of faith is aroused and sustained by the Spirit of truth. It is exercised under the guidance of the sacred teaching authority, in faithful and respectful obedience to which the people of God accepts that which is not just the word of men but truly the word of God.(112) Through it, the people of God adheres unwaveringly to the faith given once and for all to the saints,(113) penetrates it more deeply with right thinking, and applies it more fully in its life."