Air carrier First Officer reported while taxiing onto the runway; the aircraft slid on the icy surface. The Captain used reverse thrust and braking to stop the aircraft and it did not depart the runway. Reporter stated the RCAM values were incorrect and runway surface was a sheet of ice.

Narrative

Flight XXX; Weather: 050/16G26 1/2 -SN BR FG BLSN OVC09 -4/-1 A3013 RXX RCAM 3/3/3 TYPE II & TYPE IV Application (Holdover: XA:05-XB:00) Began Type IV XA38 (Holdover: XR43-XU38). After receiving Type II & Type IV; the Captain (CA) determined that the winds (a tailwind added to the already less than desirable weather conditions) did not favor a Runway XX departure therefore; we requested Runway XY. While taxiing (from Taxiway 1-2-Runway XY at approximately XS50); I remember thinking to myself; 'Okay; we are going nice and slow; this is not too bad; the tires are gripping nicely'. As we approached the departure end of Runway XY; the Tower cleared us for departure and the CA asked me to respond that we needed a minute and wanted to know the winds again. The CA then came to a stop and made another assessment and told me to let Tower know that we were ready. The CA started to make the left 90 degree turn to line up onto the runway; but; because we were moving so slowly; I did not realize that the CA was trying to keep the aircraft from sliding until; in fact; it was sliding and we were moving towards the right edge of Runway XY and the runway sign was at our nose. At that time; the CA deployed reverse thrust and we both applied full brake pressure. The aircraft came to a full stop at a 45 degree angle to Runway XY and approximately 2 ft. from the runway edge with the aircraft nose just shy of the runway sign. We did not depart the runway pavement and the aircraft did not make contact with any lights/markers/signs. The CA's slow taxi to line up and his quick response and reaction to the situation; averted what could have been a more serious situation. The RCAM condition reported (3/3/3) was nowhere near the actual conditions of that runway; it was a sheet of ice which; with the BLSN; was not detected until we attempted to taxi onto it.