Airline Captain reported momentary loss of aircraft directional control after encountering non-visible taxiway ice during night taxi following a landing in freezing drizzle conditions at ORD.

Narrative

ORD had experienced FZDZ. At our arrival time; temperature was 1 degree with DZ. We landed [Runway] 28C with braking action good. Surface conditions were wet; with patchy slush. I exited the runway and taxied on the parallel taxiway with no braking problems. The Controller instructed us to take Taxiway GG and cross Runway 28R. Taxiway GG has two 45-degree bends. On the first bend; I took the turn at around 8-10 knots; with no directional or control problems. Slowing further; to take the next bend and to look to the left to ensure that [Runway] 28R was clear to cross; I turned the tiller but the nose did not turn. It was obvious that the aircraft was suddenly sliding on ice. I applied maximum braking and the aircraft continued to slide for 10 to 20 feet. I attempted to apply reverse thrust to stop the aircraft; but was unable to do so. The aircraft stopped prior to the edge of the taxiway; but I could see that we were still on the taxiway and that we still had adequate clearance from the taxiway lights. I called Ground and declared braking action NIL on Taxiway GG. From there; I taxied at 5 knots or less to the gate. After landing; I called Dispatch and did a patch to Maintenance Control to inform them of the NIL braking action. The First Officer did a thorough post-flight inspection and found no damage to the aircraft anywhere. We debriefed the event and determined that the ice at Taxiway GG was not visible.