Windows container powershell not installed

When I type

docker exec -it fooId powershell

I have returned

 failure in a Windows system call: The system cannot find the file specified. 

So if i go in the container with

docker exec -it fooId cmd

launching powershell I have back that

'powershell' is not recognized as an internal or external command,
operable program or batch file.

How can I have powershell in my windows container?

I am working with Docker for Windows and running Windoes containers.