WPF ComboBox and binding

XAML:

<Grid x:Name="xDetails" >
...
 <ComboBox x:Name="CurrencyCode" 
           SelectedValuePath="CurrencyId"   
           DisplayMemberPath="ISOCode"  
           SelectedValue="{Binding BaseCurrency.Id}" 
  />
...
 </Grid>

Code behind:

ICollection<Currency> CurrencyList; // object populated elsewhere
xObject CurrentObject; // object with one field called BaseCurrency
...
CurrencyCode.ItemsSource = CurrencyList;
xDetails.DataContext = CurrentObject;


xObject definition:
public partial class xObject : DtoBase
 {
...
 [DataMember]
 public IdDisplayValue BaseCurrency
...
}


IdDisplayValue definition:
[DataContract]
 [Serializable()]
 public class IdDisplayValue : DtoBase
 {
 ...
 [DataMember]
 public int Id
...
 [DataMember]
 public string DisplayValue
...
 }


Currency definition:
public partial class Currency : DtoBase
 {
...
 [DataMember]
 public int CurrencyId
...
 [DataMember]
 public string ISOCode
...
 }