The nation's big insurers are spending millions to carry out President Barack Obama's health care overhaul even though there's a chance the wide-reaching law won't survive Supreme Court scrutiny.

It's not that health insurance companies want to bet big that the court will uphold the Affordable Care Act, but they can't afford not to. It will take at least several months and lots of resources for insurers to prepare to implement key elements of the law, which includes a controversial requirement that most Americans have health insurance by 2014.

WellPoint Inc., the nation's second-largest health insurer with 34 million members, has said it will spend $100 million this year on technology upgrades to meet the law's requirements. Aetna Inc., third-largest U.S. health insurer with more than 18 million members, says it expects to spend $50 million this year in part to upgrade software and computers.