Medicaid Third Party Liability Act This bill alters provisions related to third-party liability for medical assistance paid under the Medicaid program. Specifically, with respect to such liability, the bill: expands the definition of "responsible third party" to include, among other health insurers, the TRICARE program; eliminates special rules with respect to certain services provided to children; requires the inclusion, in a contract between a state Medicaid program and a health insurer, of certain information regarding whether the state is delegating or transferring to the insurer a right of third-party recovery; provides for the treatment as overpayment of reimbursements made by a responsible third party to a health insurer; disallows a responsible third party from denying a state's claim solely on the basis of a failure to obtain a prior authorization; imposes a timeline for a responsible third party to respond to a state's inquiry regarding a claim for payment; provides for reductions to a state Medicaid program's federal matching rate if the state fails to comply with third-party insurance requirements; and modifies other provisions related to third-party liability under the Medicaid program. Third-party liability requirements applicable under Medicaid shall also apply under the Children's Health Insurance Program (CHIP). The Centers for Medicare & Medicaid Services must: publish on its website, and annually update, best practices for assessing third-party liability; monitor and analyze efforts to assess that liability; in consultation with states, develop and make available a model uniform reporting field for identifying information related to responsible third parties; and provide other specified information and guidance to states.