The FASB made an announcement and the SEC has now put on its web sitethe 2011 US GAAP Taxonomy making it allowed for use for SEC XBRL filings.
I submitted a test filing to the SEC previewer yesterday which used the 2011 US GAAP taxonomy which was accepted.
This blog postpoints to a number of resources which are helpful in using this new taxonomy. In particular check out the reference implementation, the reorganized version of select portions of the 2011 taxonomy, and the SEC XBRL Filing Primer.