Source: Board of Governors of the Federal Reserve System (US)  

Release: H.10 Foreign Exchange Rates  

Units:  Index Jan 1997=100, Not Seasonally Adjusted

Frequency:  Daily

A weighted average of the foreign exchange value of the U.S. dollar against the currencies of a broad group of major U.S. trading partners.
Broad currency index includes the Euro Area, Canada, Japan, Mexico, China, United Kingdom, Taiwan, Korea, Singapore, Hong Kong, Malaysia, Brazil, Switzerland, Thailand, Philippines, Australia, Indonesia, India, Israel, Saudi Arabia, Russia, Sweden, Argentina, Venezuela, Chile and Colombia.
For more information about trade-weighted indexes see http://www.federalreserve.gov/pubs/bulletin/2005/winter05_index.pdf.