Office 365: Sharing calendars outside your organization

Go into your Office 365 portal and navigate to the 'Exchange Admin' center.

Then go to 'Organization' > 'Sharing'

Edit the default policy.

Select 'All calendar appointment information...' and 'Save'.

Go into Outlook, highlight your calendar and click 'Share Calendar' on top menu.

Send shared calendar to whomever you want, choosing the appropriate level of detail.