The FASB does not define a US GAAP chart of accounts.
Companies may define any chart of accounts provided it is consitent US GAAP recognition guidance (link: asc.fasb.org).
eXtensible Business Reporting Language is a reporting language.
"In a nutshell, XBRL provides a language in which reporting terms can be authoritatively defined. Those terms can then be used to uniquely represent the contents of financial statements or other kinds of compliance, performance and business reports. XBRL lets reporting information move between organisations rapidly, accurately and digitally" (link: xbrl.org).
It is not a chart of accounts.
As XBRL is intended to be used for reporting purposes, it is not designed to serve as a chart of accounts. Nevertheless, companies occasionally try to use the taxonomy for this purpose. To reflect this practice, this site presents a chart of accounts strictly based on the FASB XBRL taxonomy although it does not recommend its use in practice.