This article deals with idiomaticity of a special type of collocations—binomials—on Russian language material. A corpus study was conducted to obtain quantitative data on the frequency, fixity, and the strength of attraction between words of 147 Russian binomials with the structure “A i B” (where A, B are nouns, and “i” is a coordinating conjunction “and”). Statistical methods were used to reveal the measures of mutual information (MI) and logarithmic probability (log-likelihood). The data analysis allows us to conclude that the process of ideomatization is influenced by both the frequency of the entire collocation and the frequency of the words included in this collocation. Therefore, the collocative strength of the binomial was singled out as a statistical sign of idiomaticity. Overall results support the idea of a holistic storage of binomials in mental lexicon. High-frequency binomials with collocative power are included in the process of ideomatization and are stored in the mental lexicon as a whole.