The flight crew noted a loss of aileron control (felt frozen), while cruising at FL 370. They were able to make heading changes by using the rudder and elected to divert to Kansas City (MCI). The airplane had been exposed to rain and standing water before the flight. The crew felt the loss of aileron control may have been due to frozen water in the control system. During descent to MCI, above freezing air temperatures were encountered, and control of the ailerons gradually returned until full control was regained. An uneventful landing was made at MCI. Investigation revealed worn aileron control bearings in the lateral control actuator system. The worn bearings were tested by soaking in water and freezing. Water penetrated a bearing housing and froze inside the bearing race, disabling the bearing. Subsequent disassembly of the bearing disclosed corroded and worn ball bearings. Boeing Service Letter (767-S-27-094) and Service Bulletin 767-27-0128 were issued to address inspection/replacement criteria of the bearings.