Detroit's bankruptcy filing has pensioners worried. (Bill Pugliano/Getty Images)

Americans aren't suddenly saving a lot more of their incomes. But it looks that way, thanks to a change in how the federal government accounts for pension plans -- a change that, if you're not careful, could lead you to think the nation is better set for retirement than it actually is.

Until Wednesday morning, the Commerce Department pegged America's personal savings rate at 4.1 percent for 2012. An every-five-years revision to how the department measures the components of Gross Domestic Product pushed that savings rate up; now it's 5.6 percent for 2012. The same change makes savings look much stronger before the Great Recession, too: The rate for 2002 was revised up from 3.5 percent to 5 percent. For 2005, it rose from 1.5 percent to 2.6 percent.

That money isn't necessarily real. The Bureau of Economic Analysis didn't find hundreds of billions of dollars stuffed in Americans' mattresses. It decided to start counting all pension promises as savings in the bank.

That change is called accrual accounting, and as officials at the BEA point out, it's a well-accepted practice in the corporate world. The idea is that if a company or, more likely in this case, a government entity, has agreed to provide pension benefits to workers in the future, the value of those benefits should count as savings for the worker, even if the company or the government doesn't project an income stream large enough to cover all those pension IOUs.

The promises that aren't backed by an income stream are called unfunded liabilities, and by changing how it counts them, the government added almost $200 billion to the nation's personal savings for 2012.

The catch is, what if those promises don't come true? The accounting change was made shortly after Detroit became the largest U.S. city to file for bankruptcy, in part due to the unfunded liabilities in its pension plan, raising questions over whether pensioners will actually receive the benefits they've been promised. Signs point to more strains on state and local government pension funds down the road.

Americans tell pollsters they're increasingly anxious about retirement security. That's a big problem for workers and policymakers to tackle, and one that an accounting change isn't going to ease.