Investing.com - ExxonMobil (NYSE:XOM) stock has slumped for most of the past year, but one Wall Street firm has added the energy giant to its list of best investment ideas, calling it a great buying opportunity. Bank of America/Merrill Lynch likes ExxonMobil's potential to double its cash flow in the coming years, and expects the company to resume share buybacks in 2018.The firm reiterated its buy rating and $100 stock-price target, and also added the company to its US 1 top ideas list.BoAML said ExxonMobil has a "growth outlook that is unprecedented amongst among the large-cap U.S. oils."Though crude oil prices have rebounded in the past year, shares in ExxonMobil and other big energy companies haven't benefitted much.The stock is down 7% in the past 12 months and 13% from its January 2018 high.