Seattle-based WaMu reported $307.2 billion in assets at the second-quarter close. At the last head count, it employed 43,198 workers in 2,239 retail branches and offices in 15 states. As a result, JPMorgan becomes the nation's biggest bank by deposits.

In last night's press release, the Office of Thrift Supervision said WaMu had racked up a net deposit loss of $16.7 billion as of Sept. 24. The federal agency said significant deposit outflows began Sept. 15 "because of adverse events in the financial markets." The feds said there essentially was no time to "augment capital, improve liquidity or find an equity partner." The feds seized WaMu after it became apparent it most likely would be unable to pay obligations and meet operating liquidity needs.

WaMu's branches are open today and depositors have full access to all their accounts, according to the FDIC. JPMorgan's purchase does not include claims by equity, subordinated and senior debt holders, the FDIC said. JPMorgan, which had its own investment bank value the mortgages, is betting the benefits from the remaining deposits outweigh the cost in loan losses.