Hurricane Sandy's economic toll is poised to exceed $20 billion after the biggest Atlantic storm slammed into the Eastern U.S., damaging homes and offices and flooding subways in America's most populated city.

The total would include insured losses of about $7 billion to $8 billion, said Charles Watson, research and development director at Kinetic Analysis Corp., a hazard-research company in Silver Spring, Maryland. Much of the remaining tab will be picked up by cities and states to repair infrastructure, such as New York City's subways and tunnels, he said.

"I think it is disproportionate going into the public sector side," Watson said by telephone. The real extent of the damage won't be known until the flood recedes and workers can inspect subway and utility tunnels.