Your guide to interpreting the 2017 US GAAP Taxonomy

US GAAP 2017 Taxonomy

Effective March 6, 2017, the following updates to the US GAAP Taxonomy have been approved by the SEC and are supported for filing by EDGAR.

What are the big changes this year?

The 2017 Taxonomy contains a large number of changes this year, including a few new technical features that greatly modify the traditional approach to XBRL tagging. To facilitate learning, the Financial Accounting Standards Board (FASB) has published new taxonomy implementation guides concurrent with the new taxonomy to provide crucial information.

The changes are primarily due to a few accounting standard updates (ASU), as well as taxonomy remodeling in a couple of areas as a result of the FASB’s efforts to streamline dimension and address its limitations.

Over 900 new elements have been added, and almost 1,300 existing elements have been modified. The main sources of these changes came from a few ASUs, including Leases, Revenue from Contracts with Customers, Financial Instruments, as well as dimensional remodeling of Retirement Benefits, and Consolidating and Ownership disclosures.

  New Elements Changed Elements
Leases (Topic 842) 375 260
Revenue from Contracts with Customers (Topic 606) 135 160
Financial Instruments (Subtopic 825-10) 25 25
Retirement Benefits 70 400
Consolidating/Ownership Disclosures 2 n/a

Of these changes, the taxonomy structural changes on Consolidating/Ownership disclosures and Retirement Benefits are especially impactful because they require significant remapping of previously tagged disclosures. The updates involved breaking up part of the existing Legal Entity [Axis] into two new axes, while retaining the Legal Entity [Axis] itself for a specific usage. Any disclosures tagged with the Legal Entity [Axis] previously would need to be reevaluated as to the required action items.

Retirement Benefits is the other area of significant remodeling. Three existing axes were deprecated, and five new axes were added. The migration from the old axes to the new ones will depend on the information being tagged and the applicable axis-member element combinations involved.

Almost half of Wdesk filers are impacted in these areas—a significant portion, with over 10 percent of their XBRL filings impacted.

In addition to these regular taxonomy modifications, the 2017 Taxonomy also introduces some new technical features that US GAAP XBRL filers have not seen in the past. The key items include extensible list, typed dimensions, and taxonomy templates.


Extensible list is a new element type that is intended for associating additional information with a fact that is not disaggregating an item into its components. Using the extensible list element requires the information being tagged to be an element in the standard or extended taxonomy before it can be applied as the fact value of the extensible list item. There are 27 new extensible list elements included in the 2017 Taxonomy.

Although the number of extensible list elements added may not seem very high, it does add a level of complexity in one’s modeling decision. The extensible list elements included in the 2017 Taxonomy also exist as axes.

For example in, Defined Benefit Plan, Tax Status [Extensible List], and Retirement Plan Tax Status [Axis]: Whether the extensible list or the axis should be utilized to tag a disclosure will depend on whether the disclosure is communicating one component of an item or some additional information about a whole item. Filers should follow the FASB’s taxonomy implementation guides to exact the intended usage of these extensible list elements.


Typed dimension is a different kind of dimension than the traditional axis that US GAAP XBRL filers are familiar with. Typed dimension constrains the format of its members, so any new member addition must be created in a specific format or sourced from existing taxonomy elements. The only new typed dimension is included in the new taxonomy group for Revenue for the remaining revenue performance obligation disclosure. This new typed dimension is a date typed axis whose members must be in the CCYY-MM-DD format.

Filers should note that these new types of XBRL items are limited to the specific usages, as illustrated in the implementation guides. Unlike other XBRL elements, filers cannot extend their own extensible lists or typed dimensions.

Taxonomy templates are XBRL presentation outline examples that go with the disclosure examples in the new implementation guides. They are provided in the FASB’s taxonomy viewer to facilitate understanding of the intended tagging approach for the disclosures to which the templates relate.

What does this mean for you?

As you can see, the 2017 Taxonomy is full of excitement! Given the magnitude of the changes introduced this year, migration to the new taxonomy is expected to require much higher effort and training for most filers compared to the prior years. Filers should carefully evaluate the changes’ impacts on their documents before proceeding with the migration.

There are a number of available resources on from the Financial Accounting Standards Board:

Taxonomy Release Notes
Taxonomy Technical Guide
Taxonomy Implementation Guides

Make sure to review these materials, so you know what changes are likely to affect your filings. Look for additional learning opportunities from the FASB and Workiva.

Also, if you're considering creating an extension for something that is in the new taxonomy before you've made the transition, it is best to copy the exact element name and other information associated with the new element. Many data quality validation rules as well as taxonomy migration paths are dependent on the exact element ID, including capitalization. Copying the exact information would ensure compatibility with these tools.

The SEC strongly encourages you to use the most current version of the taxonomy for your filings. Don't wait until the last minute—keep in mind that once the 2017 Taxonomy is released, filers have a short grace period to move off of the 2015 version before it is removed from the SEC’s supported taxonomies for filing. This is currently not expected to occur before June 2017.

To see the taxonomy and release notes including all of the 2017 changes, visit the FASB site.

anna kwok

About the author

Anna Kwok
Anna Kwok is Vice President of Professional Services at Workiva. Prior to Workiva, she served as Vice President, Controller, and FP&A Manager at various public and private companies. She has 20+ years of experience in SEC reporting and accounting as well as financial planning and analysis.