It is important for a humanoid robot to be able to move its body without falling down even if the target motion takes its center of mass to the limits of the support polygon. Usually the center of mass is overconstrained to keep balance, but this can make fast motion of the robot upper body or tasks that are far away from the reachable space unfeasible. To achieve these tasks that challenge the robot balance, this paper proposes the integration of the capture point (CP) in the operational-space inverse dynamics control framework. Then, if balance is about to be lost, a good place to step to will be determined preventing the robot from falling down. Moreover, the control of the CP as a task (or constraint) guarantees that it is kept within certain limits, allowing the foot to have time to safely step to it before the robot falls. An advantage over other methods is the transparent integration of the CP letting the robot be able to simultaneously move its whole body satisfying other tasks. The method has been tested in simulation using the dynamic model of HRP-2.