However, looking at the Committee’s draft memo (page 75 and after), such dramatic headlines need to be taken with a ton of salt. Substantive assurance costs (if any) are likely to arise only if the production of XBRL formatted data were implemented in the least competent way imaginable, i.e., by means of what might be described as a parallel XBRL track of accounting. To assume that this is the default practice would not exactly reflect high expectations with regards to the professional competence of finance departments.
One of the basic tenets of XBRL disclosure is that it is in fact disclosure neutral, i.e., the numbers displayed in an XBRL instance document are identical to what is reported on (electronic) paper. For as long as XBRL filing is not the exclusively permitted way of filing, assurance of disclosure neutrality probably satisfies the needs of most users of financial statements. In a reasonably well structured accounting & auditing cycle, such assurance should come cheaply.