WASHINGTON, April 21 (Reuters) - The Democratic Senate financial reform bill would reduce the U.S. budget deficit by $21 billion over the next 10 years, according to a cost estimate by the Congressional Budget Office obtained by Reuters on Wednesday.

The estimated reduction in the budget deficit over the 2011-2020 period stems largely from charging the financial industry assessments for a fund to liquidate large, troubled financial firms, the office said.

The bill authored by Senate Banking Committee Chairman Christopher Dodd is designed to ensure that no financial firm is too big to fail. (Reporting by Rachelle Younglai and Karey Wutkowski; Editing by Leslie Adler)