How's this for action. Northern Trust -- the bank TMZ exposed this week for throwing a series of lavish parties and concerts in L.A. -- is giving back the $1.6 billion in federal bailout money!

We had our cameras out as the bank hosted fancy dinners for hundreds of clients and employees. We had video of the

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concert it threw after closing down the House of Blues. And then there were concerts by

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, as well as Earth, Wind & Fire ... and the Tiffany gift bags for the ladies.

The story triggered a furor in D.C. ... Congressman Barney Frank demanded that Northern Trust repay the money it blew.

Outrageously, the bank didn't even ask for the bailout money in the first place. But now, under pressure, Northern Trust CEO Frederick Waddell sent a letter to members of the House Financial Services Committee, saying his bank will repay the government funds "as quickly as prudently possible."