NT ID field not showing NTID in the database

Hello All,

I have a some list of tables in which I have a column called "NT_ID" in most of the tables. Nvarchar(max)

We are using NT Authentication in our project.

Now I have used the following code in C# to capture the logged in NT user name

string usrName = System.Security.Principal.WindowsIdentity.GetCurrent().Name;

So i am inserting this value to most of my tables. 

But in the NT ID field of the table I am seeing the following:

NT AUTHORITY\IUSR
NT AUTHORITY\NETWORK SERVICE
IIS POOL

We have hosted this project via sharepoint. 

We have the following setting under web config: identity impersonate = true.