The bank outlined plans for Merrill Edge Guided Investing, a new service meant to combine Merrill Edge’s online brokerage platform with Merrill Lynch’s human advisers’ wealth-management expertise. The unit of the Charlotte, N.C.-based bank was formed six years ago and has amassed $132 billion in assets, currently serving clients online, through hundreds of domestic Bank of America branches and through centralized call centers. In starting its own robo service, Merrill is entering a market pioneered by startups including Betterment LLC and Wealthfront Inc. as a response to investors’ demand for low-cost advice in an era of low expected returns. Regulatory changes, including the Labor Department’s fiduciary rule, also implicitly favor low-cost advisory services willing to act in the best interests of their clients. The company said last year that it was considering an automated advice service.