8. A method for generating markup language to represent a calculation relationship among a plurality of facts, the method carried out by one or more computing devices, the method comprising: parsing markup language of an extensible business reporting language (XBRL) instance document containing the plurality of facts, wherein each fact comprises a value tagged with XBRL tags according to one of a plurality of XBRL concepts, one or more relationships among the plurality of XBRL concepts is defined by markup language contained in a taxonomy document; based on the parsing, determining that at least two facts of the plurality have the same XBRL period type and XBRL period date, determining that the at least two facts have different units of measure; based on the determination that the at least two facts have the same XBRL period type and same XBRL period date but have different units of measure, defining a fact-based calculation relationship between the at least two facts; generating markup language that represents the defined calculation relationship; and modifying the taxonomy document with the generated markup language.
8. A method for generating markup language to represent a calculation relationship among a plurality of facts, the method carried out by one or more computing devices, the method comprising: parsing markup language of an extensible business reporting language (XBRL) instance document containing the plurality of facts, wherein each fact comprises a value tagged with XBRL tags according to one of a plurality of XBRL concepts, one or more relationships among the plurality of XBRL concepts is defined by markup language contained in a taxonomy document; based on the parsing, determining that at least two facts of the plurality have the same XBRL period type and XBRL period date, determining that the at least two facts have different units of measure; based on the determination that the at least two facts have the same XBRL period type and same XBRL period date but have different units of measure, defining a fact-based calculation relationship between the at least two facts; generating markup language that represents the defined calculation relationship; and modifying the taxonomy document with the generated markup language. 9. The method of claim 8 , further comprising: parsing the markup language of the taxonomy document to identify a concept element having a preferred label role value indicating that facts associated with the concept are in a calculation relationship, wherein parsing the markup language of the instance document comprises parsing the markup language of the instance document to identify facts tagged with the identified concept.