If + duration calculation issue in query editor

Hello!

Does someone have an experience combining if statment with duration in query editor? 

I am trying to calculate the lenght of employment, my formula looks like this:

#"Inserted Duration"= Table.AddColumn(#"Added Conditional Column3", "Duration", each if [Employee Status] = "Terminated" then Date.From([Employment Details Termination Date] - [Employment Details Start Date], type duration) else each Date.From(DateTime.LocalNow() - [Employment Details Start Date], type duration)),

My formula is probably completely wrong since the only result I get is "Error". 

Appreciate any feedback! 

Thank you!