Initialization issue with the structuremap

Currently am using the structure map for injecting the transactionid which is a uniqie Guid that needs to be created each time 
x.For<ITransaction>() .Use<Transaction>() .Ctor<string>("transactionId").Is(Guid.NewGuid().ToString()) .Ctor<string>("transactionType").Is(settings["TransactionTypeValue"]); With in controller ITransaction is passed as an argument and getting the TransactionId . But am not getting the unique Guid whenever the action method is invoked . Its all set while loading the application and the same value is coming up every time. How can i generate unique Guid each time when the action method is getting called using the structure map configuration. Please help me out