XMLmind Word To XML (w2x) can automatically convert DOCX files to DITA maps and topics.

Because w2x does not leverage MS-Word style names to do its job, you'll get good results out of the box. However, in some cases, you'll have to map a custom MS-Word style (e.g. "CodeSample") to an XML element (e.g. <codeblock>) to get excellent results.

Fortunately, desktop application w2x-app, which comes with new XMLmind Word To XML v1.2, has now a setup assistant including an easy-to-use style mapper (see screenshot below).