Here is a link to a web page provided by the state of Texas. The web page contains links to the financial reports of a number of the larger cities in Texas. You can go to this web page, click on a link, and go read a financial report in the form of a PDF file.
The financial report is called a CAFR (Comprehensive Annual Financial Report). I don't know the exact rules, but I believe it is the case that the approximately 88,000 state and local governmental entities within the United States are required to file this report annually with the US Census Bureau.
The state of Oregon undertook a project to experiment with expressing this CAFR report in an XBRL format. You can obtain a copy of that study here.
Try and do a comparison of, oh let's say three different Texas cities using those PDF files. Can it be done? Absolutely. All one needs to do is rekey the information.
The web page has a title "Transparency by Texas Cities". You can clearly see how XBRL can contribute to transparency by making it vastly easier to get at the information within these types of PDF based financial reports.
Imagine if the financial information of all 88,000 state and local governmental entities were put into the type of system the SEC has created for public company financial information, their new IDEA system. Here is a prototype of how using this information could work.
That would dramatically increase transparency! Imagine the analysis which could be done, how the information could be used by economists and academics for all sorts of things, and imagine the view voters could have into the governments which spend their money.
Financial information of the agencies and departments of the US Federal Government could also be made available in this manner.