42 CFR § 411.4 - Services for which neither the beneficiary nor any other person is legally obligated to pay.
(a) General rule. Except as provided in § 411.8(b) (for services paid by a governmental entity), Medicare does not pay for a service if -
(1) The beneficiary has no legal obligation to pay for the service; and
(2) No other person or organization (such as a prepayment plan of which the beneficiary is a member) has a legal obligation to provide or pay for that service.
(b) Special conditions for services furnished to individuals in custody of penal authorities. Individuals who are in custody include, but are not limited to, individuals who are under arrest, incarcerated, imprisoned, escaped from confinement, under supervised release, on medical furlough, required to reside in mental health facilities, required to reside in halfway houses, required to live under home detention, or confined completely or partially in any way under a penal statute or rule. Payment may be made for services furnished to individuals or groups of individuals who are in the custody of police or other penal authorities or in the custody of a government agency under a penal statute only if the following conditions are met:
(2) The State or local government entity enforces the requirement to pay by billing all such individuals, whether or not covered by Medicare or any other health insurance, and by pursuing collection of the amounts they owe in the same way and with the same vigor that it pursues the collection of other debts.