Transition from Marketplace plan to Medicare.

Requires an insurer or health maintenance organization that provides coverage under an Affordable Care Act Marketplace (Marketplace) plan to provide to each individual covered under the Marketplace plan, not more than two months before the birthday on which the individual will become 65 years of age, a written message that includes: (1) a statement that the individual will be eligible to enroll in Medicare during the individual's initial enrollment period, which begins three months before the individual becomes 65 years of age; (2) a statement advising the individual that, in most cases, someone covered by a Marketplace plan will want to end their Marketplace coverage upon becoming eligible for Medicare; and (3) detailed instructions that the individual may follow to cancel the individual's Marketplace plan. Prohibits an insurer or health maintenance organization from collecting a premium for an individual's Marketplace plan coverage after the earlier of: (1) the birthday on which the individual becomes 65 years of age; or (2) the date on which the individual's Medicare coverage begins. Requires an insurer or health maintenance organization to return the part of any premium that was collected for an individual's Marketplace plan coverage but was not earned as of the birthday on which the individual becomes 65 years of age. Empowers the insurance commissioner to impose a civil penalty on or suspend or revoke the certificate of authority of an insurer or health maintenance organization that commits a violation.