Americium, which stands directly after plutonium in the periodic table, represents a strategically important element. As a consequence investigations of its magnetic properties, particularly its magnetic susceptibility, are of great scientific importance. In the present study we develop a self-consistent procedure that combines ab-initio calculations of electronic structure in terms of LDA + U + SO method with the generalized spin-fluctuation s(p)df-model. In terms of this approach we have calculated the densities of states and temperature dependencies of magnetic susceptibility of americium. These calculations enabled to explain the experimental data from two independent sources. It is shown that the unconventional transition from Curie-like to Pauli-like magnetic susceptibility in americium is caused not by presence of magnetic impurities, but by the balance change in the number of localized and itinerant electronic states. Thus the results obtained can have practical applications for the estimations of concentration of impurities and defects (including radioactive) in americium and its compounds.