Center for Medicare and Medicaid Services

The Biogen Inc., headquarters is shown in Cambridge, Mass. Medicare says it will limit coverage of a $28,200-per-year Alzheimer's drug whose benefits have been questioned. Steven Senne/AP hide caption

Medicare Advantage health plans have enrolled nearly 27 million members, or about 45% of people eligible for Medicare. A recent analysis finds Medicare overpaid the private health plans by more than $106 billion from 2010 through 2019 because of the way the plans charge for sicker patients. Innocenti/Image Source/Getty Images hide caption

Medicare is funded by a combination of money paid directly to the federal government from paychecks and taxes paid by working Americans. Most dental procedures and tests are not covered under traditional Medicare. Cavan Images/Getty Images hide caption

Medicare Advantage, a fast-growing private alternative to original Medicare, has enrolled more than 26 million people. Humana Inc. is one of the largest of these insurers. While popular with seniors, Medicare Advantage has been the target of multiple government investigations. Pablo Martinez Monsivais/AP hide caption

Medicare's overhauled Plan Finder debuted at the end of August. But health care advocates and insurance agents say the website has had big problems ever since, including inaccurate details about prices, which drugs each plan covers and their dosages. Catie Dull/NPR hide caption

Colorado estimates that about 15% of the 12 million letters it sends to beneficiaries of public assistance programs each year are returned unopened, left to pile up in county offices like this one in Colorado Springs. That amounts to about 1.8 million pieces of undelivered mail each year statewide. Markian Hawryluk/KHN hide caption

Medicare Advantage health plans, mostly run by private insurance companies, have enrolled more than 22 million seniors and people with disabilities — more than 1 in 3 people who are on some sort of Medicare plan. Pablo Martinez Monsivais/AP hide caption

In rugged, rural areas, patients often have little choice about how they'll get to the hospital in an emergency. "The presence of private equity in the air ambulance industry indicates that investors see profit opportunities," a 2017 report from the federal Government Accountability Office notes. pidjoe/Getty Images hide caption

If a doctor is found to be ordering too many MRI or CT scans or other imaging tests for Medicare patients, a federal law is supposed to require the physician to get federal approval for all diagnostic imaging. But the Trump administration has stalled the law's implementation. laflor/Getty Images hide caption

"As deductibles rise, patients have the right to know the price of health care services so they can shop around for the best deal," says Seema Verma, who heads the Centers for Medicare & Medicaid Services and announced the Trump administration's plan this week. Kevin Wolf/AP hide caption

Medicare Advantage plans, administered by private insurance companies under contract with Medicare, treat more than 22 million seniors — more than 1 in 3 people on Medicare. Roy Scott/Ikon Images/Getty Images hide caption

Over the past decade, hospitals have been rapidly building outpatient clinics or purchasing existing independent ones. It was a lucrative business strategy because such clinics could charge higher rates, on the premise that they were part of a hospital. Medicare's recent rule change puts a damper on all that. Hero Images/Getty Images hide caption

Both Democrats and Republicans have introduced proposals that would impose a cap on out-of-pocket costs of prescription drugs for Medicare patients. But it's still unclear whether those moves will gain a foothold. Jeffrey Hamilton/Getty Images hide caption

If you earn too much to get a subsidy to help defray the cost of health insurance, you might find a less expensive policy off an exchange. PeopleImages/Getty Images hide caption

Cashiers, cooks, delivery people, fast-food workers and their supporters rallied outside New York City Hall in 2017. Their influential union, the Service Employees International Union, also includes about half a million home health aides. Pacific Press/LightRocket/Getty Images hide caption

Free-standing ERs tend to have lower standby costs than hospital-based facilities that have to be ready to treat dire injuries. But the free-standing ERs typically receive the same Medicare rate for emergency services. sshepard/Getty Images hide caption

The Centers for Medicare and Medicaid Services — and its controversial center for innovation — is part of the U.S. Department of Health and Human Services, and has its headquarters outside D.C., in Woodlawn, Md. Jay Mallin/Bloomberg via Getty Images hide caption