  Quantum correlations forms a subset of the set of nonsignaling boxes. This
allows us to characterize quantum correlations as a convex combination of the
extremal boxes of the nonsignaling polytope which are Popescu-Rohrlich boxes
(maximally nonlocal boxes) and local deterministic boxes. There exists multiple
decomposition of quantum correlations in the context of the nonsignaling
polytope. I find that the existence of Popescu-Rohrlich box decomposition for
local boxes associates two notions of discord which capture nonclassicality of
quantum correlations originating from Bell nonlocality and EPR-steering. I
introduce, Bell and Mermin discord, and demonstrate that any bipartite
nonsignaling box admits a three-way decomposition. This decomposition allows us
to isolate the origin of nonclassicality into three disjoint sources: a
Popescu-Rohrlich box, a maximally local box that detects EPR-steering, and a
classical correlation. Interestingly, I show that all non-null quantum discord
states which are neither classical-quantum states nor quantum-classical states
can give rise to nonclassical correlations which have non-null Bell and/or
Mermin discord for suitable noncommuting measurements. I introduce two notions
of genuine discord, which are the generalizations of Bell and Mermin discord to
the multipartite boxes, to characterize the presence of genuine nonclassicality
in multipartite quantum correlations.
