Did you mean IDML? Is CS6 patched to at least 8.0.2?
With CS6 and CC from the cloud you can open an INDD file which was created with a later version when it was saved with the latest updated version. CS6 and CC from the cloud send this file to Adobe's Server and get back a converted file. That's said, you need internet connection.
If you are a CS6 user, but not in the cloud, you have to require an IDML file saved from CC or CC 2014.
CS6 from the CC and CS6 perpetual version are different versions.