Additional Study Information: The purpose of this study is to evaluate how well the study drug ABT-199 works and safety of ABT-199 in subjects with Chronic Lymphocytic Leukemia (CLL) whose cancer has come back (relapsed) after treatment or no response (refractory) to treatment with B-cell receptor signaling pathway inhibitor therapy, namely Ibrutinib and/or Idelalisib. In addition, substances found in the blood, bone marrow and tissue (biomarkers) that may indicate the effects or progress of the leukemia and the activity of ABT-199 will be studied.