It also surpassed nuclear. That sector has been fairly steady while coal is dropping. U.S. Energy Information Administration - EIA - Independent Statistics and Analysis This is a handy site for looking into more details. Electricity Data Browser
Looking at the linked data browser (not the shorter period charts in the article), it looks like coal source peaked in 2005-7, and has declined by almost 60% since. As a fraction of total production, it fell from 49% then to 20% last year, and expected to be 17% this year. The browser also suggests that new wind and solar have covered a bit more than all load growth since 2001.
