The joint company would include 12.3 million Medicaid members, 4.8 million Medicare Advantage and Part D members and 1.5 million members in its ACA plans, according to the investor presentation. Centene and WellCare estimate that merging will create $500 million in cost synergies in the joint company's second year, bolstered by greater scale in the government business. RELATED: Centene still bullish on ACA exchanges despite legal challenges to the law In 17 states, the joint company would offer insurance products in all three of those markets, according to the presentation.