  We develop the holographic formulation of transport in strongly coupled
two-layer systems. We identify a dc conductivity, sigma^dc, that is finite even
in a translationally invariant setup, and universal for CFTs with a gravity
dual. The thermoelectric conductivity and heat conductivity are fully
determined by the electrical conductivity matrix, as a consequence of Ward
identities. We use the memory-matrix approach for double-layer systems,
together with Ward identities, to show that sigma^dc - extended to finite
frequency - has no Drude peak and, similarly, that its universal value is
unaffected if translation invariance is softly broken.
