Concept:
Rene Descartes is famous for rationalism and mind-body dualism.
He distinguished between:
\[
\text{Mind} = \text{thinking substance}
\]
and
\[
\text{Body} = \text{extended substance}
\]
Step 1: Check Cogito ergo sum.
Descartes' famous statement is:
\[
\text{Cogito ergo sum}
\]
which means:
\[
\text{I think, therefore I am}
\]
So, option (B) belongs to Descartes.
Step 2: Check God as substance.
Descartes accepted God as an infinite and perfect substance.
So, option (C) belongs to Descartes.
Step 3: Check interactionism.
Descartes believed that mind and body interact with each other.
So, option (D) also belongs to Descartes.
Step 4: Identify the incorrect idea.
Mind and body are not absolute substances in the same sense as God.
For Descartes, God is the absolute infinite substance, while mind and body are finite created substances.
So, the statement that mind and body are absolute substances does not properly belong to Descartes' philosophy.
Hence:
\[
\boxed{\text{(A)}}
\]