The purpose of this study is to find out what effects (good and bad) treatment with a drug known as decitabine has on patients and their leukemia after they have received standard combination chemotherapy treatment for acute myeloid leukemia (AML). Standard combination chemotherapy will be followed by the experimental part of this study, treatment with decitabine to prevent relapse. Decitabine is FDA approved, however its use in this study is investigational. Decitabine has shown to have anti-leukemia activity in patients with active leukemia, but its role in preventing relapse in patients who are in remission (that is, who show no evidence of leukemia) has not been studied.