The biggest U.S. banks including JPMorgan Chase & Co. and Citigroup Inc. are lending the smallest portion of their deposits in five years as cash floods in from savers and a slow economy damps demand from borrowers.

The average loan-to-deposit ratio for the top eight commercial banks fell to 84 percent in the fourth quarter from 87 percent a year earlier and 101 percent in 2007, according to data compiled by Credit Suisse Group AG. Lending as a proportion of deposits dropped at five of the banks and was unchanged at two, the data show.