Private Sub Worksheet_Change(ByVal Target As Range)
Dim Deb As Integer, Fin As Integer
If Not Intersect(Target, Range("A:A")) Is Nothing And InStr(Target, Chr(10)) > 0 Then
Target.Font.Underline = xlUnderlineStyleNone
Deb = InStrRev(Target, Chr(10)) + 1
Fin = Len(Target) - Deb + 1
Target.Characters(Start:=Deb, Length:=Fin).Font.Underline = xlUnderlineStyleSingle
End If
End Sub