Short answer: Most U.S. health plans cover little or nothing abroad except, in some cases, emergencies. Original Medicare generally does not cover care outside the U.S. For international trips, consider travel medical insurance.
Standard employer and individual plans are designed around U.S. provider networks. Some will reimburse emergency care received abroad, but you typically pay up front and file for reimbursement, and routine care is usually not covered.
Original Medicare (Parts A and B) generally does not cover care outside the United States, with very limited exceptions. Some Medicare Advantage plans and certain Medigap policies include limited foreign travel emergency benefits, often with a deductible, coinsurance, and a lifetime cap.
If you are traveling internationally, a short-term travel medical policy can cover emergency treatment and, importantly, medical evacuation, which can cost tens of thousands of dollars and is rarely covered by standard plans. Always confirm the specifics with your insurer before you go.