The invention relates to a composition for treating keratin substances, in particular the hair, containing, in a cosmetically and/or dermatologically acceptable aqueous medium, at least: a) one zwitterionic polymer resulting from the copolymerization of at least one monomer of formula (I):  in which R1 and R2, which may be identical or different, represent a hydrogen atom or a methyl radical, and R3, R4 and R5, which may be identical or different, represent a linear or branched alkyl radical containing from 1 to 4 carbon atoms, Z represents an NH group or an oxygen atom, n is an integer from 2 to 5, A− is an anion derived from an organic or inorganic acid, and at least one monomer of formula (II): R6—CH═CR7—COOH  (II)  in which R6 and R7, which may be identical or different, represent a hydrogen atom or a methyl radical; the said polymer being soluble in water to a concentration of 1% by weight at a pH below 6 and at 20° C.; b) one non-amino, non-volatile, water-insoluble silicone with a viscosity of greater than 3×10−5 m2/s (300 centistokes).