Increased penetration of flexible loads and distributed resources on power distribution circuits will lead to possibility of aggregating such small distributed resources for several grid services both at the distribution and transmission levels. This will lead to increased interaction of transmission and distribution system operators, as well as the control actions at LV/MV grid in aggregation will have significant impact on the operations of bulk transmission systems. Therefore, lately, there has been some advancements to developing co-simulation platform for solving transmission and distribution (TD) systems simultaneously for dynamic and power flow type of studies. However, the existing co-simulation platforms base mainly on decoupled approaches. Therefore, a unified approach of solving TD (for solution benchmarking purpose) is largely missing in the literature. In this context, this paper shows initial results of a decoupled method applied for solving TD power flow co-simulation and is benchmarked against a unified solution. The case studies based on augmented 14+33 bus TD systems show that the decoupled approach is fairly accurate.