We present measurements of the inclusive branching fractions for the decays D+→Xe+νe and D0→Xe+νe, using 281pb-1 of data collected on the ψ(3770) resonance with the CLEO-c detector. We find B(D0→Xe+νe)=(6. 46±0.17±0.13)% and B(D+→Xe+νe)=(16.13±0. 20±0.33)%. Using the known D meson lifetimes, we obtain the ratio ΓD+sl/ΓD0sl=0.985±0.028±0.015, confirming isospin invariance at the level of 3%. The positron momentum spectra from D+ and D0 have consistent shapes.