WithdrwX is the correct transaction type to use to, for example, transfer cash from your investment account to your checking account.
And yes, this will reduce your investment account's cash balance. You need to sell some securities or otherwise make cash available to cover the withdrawal or you will be running a "Margin balance", provided that your brokerage allows that.
Thanks. What 'action' do I use in the transaction screen? I use withdrwX and it transfers the money to transfer account, but shows a negative cash balance?