International Business Machines Corp. plans to move about 110,000 retirees off its company-sponsored health plan and instead give them a payment to buy coverage on a health-insurance exchange, in a sign that even big, well-capitalized employers aren't likely to keep providing the once-common benefits as medical costs continue to rise.

The move, which will affect all IBM retirees once they become eligible for Medicare, will relieve the technology company of the responsibility of managing retirement health-care benefits. IBM said the growing cost of care makes its current plan unsustainable without big premium increases.

IBM's shift is an indication that health-insurance marketplaces, similar to the public exchanges proposed under President Barack Obama's health-care overhaul, will play a bigger role as companies move coverage down the path taken by many pensions, paying employees and retirees a fixed sum to manage their own care.

In notices signed by Chief Health Director Kyu Rhee, IBM has told retirees in recent weeks that to keep receiving coverage, they will need to pick a plan offered through Extend Health, a large private Medicare exchange run by New York-based Towers Watson & Co.

Medicare is the federally administered system of health insurance for people age 65 and over, and the disabled. Some people buy Medicare Advantage plans, administered by private insurers, and others buy policies to cover gaps in Medicare coverage.

IBM told retirees that its current retiree coverage will end for Medicare-eligible retirees after Dec. 31, 2013, according to documents reviewed by The Wall Street Journal and confirmed by IBM.

"Cost increases under our current retirement group health care plan are no longer sustainable for you," IBM said in the notices. "Health care costs under IBM's current plan options for Medicare eligible retirees will nearly triple by 2020, significantly impacting your premium and out of pocket costs," the notice said.

Exchanges such as Extend Health generally present policies from a range of insurers and let participants choose what best meets their needs and budgets. The aim is to create competition that keeps costs down.

Instead of subsidizing retiree health premiums directly, IBM will give retirees an annual contribution via a health retirement account that they can use to buy Medicare Advantage plans and supplemental Medicare policies on the exchange, as well as pay for other medical expenses. Retirees who don't enroll in a plan through Extend Health won't receive the subsidy.

Some companies began experimenting with exchanges around eight years ago after accounting changes forced public corporations to disclose future health-care obligations.

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