Inclusion Criteria:

          -  Histological confirmation of relapsed or refractory AML after prior anti-leukemic
             therapy by WHO classification

          -  Ineligible for cytotoxic therapy defined by the following:

             a. Age (>/=) 75 years or b. age 18- 74 years with at least one of the following
             comorbidities: i. Eastern Cooperative Oncology Group (ECOG) Performance Status of 2 or
             3 ii. Cardiac history of congestive heart failure requiring treatment or ejection
             fraction (</=) 50% or chronic stable angina iii. Diffusing capacity of the lungs for
             carbon monoxide (</=) 65% or forced expiratory volume in the first second of
             expiration (</=) 65% iv. Creatinine clearance (>/=) 30 mL/min to< 45 mL/min v. any
             other comorbidity that the physician judges to be incompatible with intensive
             chemotherapy must be reviewed and approved by the Medical Monitor before screening and
             study enrollment.

          -  Life expectancy of at least 12 weeks

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status 0-2

          -  Adequate liver and renal function

        Exclusion Criteria:

          -  Patients with acute promyelocytic leukemia (French-American-British [FAB] class M3
             AML)

          -  Known active central nervous system (CNS) involvement with AML at study entry

          -  ECOG Performance Status (>/=) 3 in patients who are (>/=) 75 years old or ECOG
             Performance Status of 4, regardless of age

          -  Prior exposure to Bcl-2 inhibitors, murine double minute 2 (MDM2) antagonists or prior
             exposure to experimental treatment targeting Raf, mitogen-activated protein kinase
             (MEK), or the mitogen-activated protein kinase (MAPK) RAS/RAF/MEK/ERK MAPK pathway

          -  Positive for hepatitis C virus (HCV), hepatitis B surface antigen (HBsAg) and known
             history of HIV, malignancy, active infection and cardiovascular diseases (CVs)

          -  Received strong cytochrome (CYP) 3A inhibitors, moderate CYP3A inhibitors, strong
             CYP3A inducers and moderate CYP3A inducers within 7 days prior to initiation of study
             treatment

          -  History of symptomatic Clostridium difficile infection within 1 month prior to dosing

        Additional arm specific exclusion criteria:

        Dose Escalation Arm A (Venetoclax and Cobimetinib):

          -  History or evidence of retinal pathology on ophthalmologic examination that is
             considered a risk factor for neurosensory retinal detachment/central serous
             chorioretinopathy (CSCR), retinal vein occlusion (RVO), or neovascular macular
             degeneration

          -  Left ventricular ejection fraction (LVEF) below institutional lower limit of normal
             (LLN) or below 50%, whichever is lower

        Arm B (Venetoclax and Idasanutlin):

          -  Received the following within 7 days prior to the initiation of study treatment:
             Strong CYP2C8 inhibitors or CYP2C8 substrates, OATP1B1/3 substrates

          -  Received the following within 14 days prior to the initiation of study treatment:
             Strong CYP2C8 inducers

          -  History of liver cirrhosis by radiologic, clinical or laboratory data, or biopsy
             despite normal liver function tests

          -  Received treatment with oral or parenteral anticoagulants/anti-platelet agents within
             7 days prior to initiation of study treatment.