  Using e+e- collisions recorded at the psi(3770) resonance with the CLEO-c
detector at the Cornell Electron Storage Ring, we determine absolute hadronic
branching fractions of charged and neutral D mesons. Among measurements for
both Cabibbo-favored and Cabibbo-suppressed modes, we obtain reference
branching fractions B(D0 -> K-pi+)=(3.91 +- 0.08 +- 0.09)% and B(D+ ->
K-pi+pi+)=(9.5 +- 0.2 +- 0.3)%, where the uncertainties are statistical and
systematic, respectively. Using a determination of the integrated luminosity,
we also extract the e+e- -> DDbar cross sections.
