Pope or Church: The Infallibility of the Ordinary Magisterium

We know about the Extraordinary Magisterium - Teaching Authority - of the Church. The Infallible Decrees and Teachings of Ecumenical Councils and Papal Ex Cathedra Declarations are well known and have been explicitly defined by the First Vatican Council. How about the Ordinary Magisterium; that Teaching of the Pope and the Bishops that is presented to us in Encyclicals, Letters, Exhortations, Homilies etc.? Is it Infallible? And if so When and under what Conditions?