3 Bishops, sharing in the solicitude for all the churches, exercise this episcopal office of theirs, which they have received through episcopal consecration, in communion with and under the authority of the supreme pontiff. As far as their teaching authority and pastoral government are concerned, all are united in a college or body with respect to the universal Church of God. They exercise this office individually in reference to the portions of the Lord's flock assigned to them, each one taking care of the particular church committed to him, or sometimes some of them jointly providing for certain common needs of various churches. This sacred synod, therefore, attentive to the conditions of human association which have brought about a new order of things in our time, intends to determine more exactly the pastoral office of bishops and, therefore, has decreed the things that follow.
Source: Christus Dominus (Vatican.va)