Twenty percent of all U.S. residential properties that had a mortgage on them were underwater at the end of December, with mortgage debt greater than what the homes were worth, according to a report released Wednesday by First American CoreLogic.

That's more than 8.3 million mortgages that were upside down at the end of the year, compared with 7.6 million three months earlier. It's a problem that is expected to get worse as home prices continue to fall.

Wall Street Journal