Time-integrated CP asymmetries in D 0 decays to the final states K − K + and π − π + are measured using proton-proton collisions corresponding to 3fb−1 of integrated luminosity collected at centre-of-mass energies of 7 TeV and 8 TeV. The D 0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in CP asymmetries between the two final states is measured to be $$ \varDelta {A}_{\mathrm{CP}}={A}_{\mathrm{CP}}\left({K}^{-}{K}^{+}\right)-{A}_{\mathrm{CP}}\left({\pi}^{-}{\pi}^{+}\right)=\left(+0.14 \pm 0.16\ \left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)\right)\%. $$ A measurement of A CP (K − K +) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D decays. It is found to be $$ {A}_{\mathrm{CP}}\left({K}^{-}{K}^{+}\right)=\left(-0.06\pm 0.15\left(\mathrm{stat}\right)\pm 0.10\left(\mathrm{syst}\right)\right)\%, $$ where the correlation coefficient between ΔA CP and A CP (K − K +) is ρ = 0.28. By combining these results, the CP asymmetry in the D 0 → π − π + channel is A CP (π − π +) = (−0.20 ± 0.19 (stat) ± 0.10 (syst))%.