Cross-Object Formulas that display referenced object fields are available as merge fields. If the user does not have permission to reference the referenced object or field, it is output as blank. Up to 5 levels up can be set as merge fields. Available in Ver.2.0 or later.
e.g. {!Opportunity.Account.BillingCity}
*In Ver.1, create a cross-object formula field in Salesforce in the child object and set the created fields as a merge field.
Instruction manual
Output Reference Object (Parent) Field