Issued: October 18, 2010
Impact: All US GAAP

This guidance is archived. See Using the Units Registry for updated Best Practice Guidance.

In the filings to date, issuers have begun to define different kinds of units besides currency. To manage this, issuers have either defined the unit in the label of the extension element, in the element name, as
an extended unit or by using US GAAP datatypes. Some examples are listed below:

An energy company used a unit of USD for the extension element
CommodityDerivativeVolumesElectricPower with a label of “commodity derivative volumes, electric power (in millions of megawatt hours) with a datatype of “xbrli:integerItemType.

Two energy companies defined megawatts (measure of power) and megawatt hours (measure of energy) in extended units using an integer datatype. The datatype powerItemType or
energyItemType is currently available in the taxonomy and should have been used. The first company used a unit of MWH for the element TotalAnnualEnergySavings with a datatype of
xbrli:integerItemType and the second company used a unit of mw for the element GenerationCapacityMegaWatts with a datatype of xbrli:integerItemType.

Ideally the unit measures should use a standard which is currently being defined by XBRL International as part of the units registry. In the interim companies should use the measure types defined in the US GAAP taxonomy in the us-types file using the xbrlus prefix i.e. xbrlus:mW. In addition any new extension elements should use the us-types provided, in this case either powerItemType or energyItemType. An example where the types was handled correctly is Edison International which used a unit measure eix:mW for the fact associated with the element PowerGeneratingCapacityOfLongTermPurchaseCommitments with a datatype of ustypes:powerItemType”.

The logic that applies in these examples also applies to other measures such as length, area, volume, volumetric flow, mass, time, temperature etc.1
1 It has been reported that some units create problems in the SEC renderer. In those cases filers have used the pure item type. If the use of a unit causes significant problems in the presentation of the XBRL renderer then the company could consider using a pure item type.