In the old days, managers were the expert. They worked their way up, learning all the various things and through experience and practice, became the expert in the area. That is what made them a suitable manager - the ability to answer questions and figure out what was wrong.
Today, departments and areas are way too complex. Think of HR - there is employment law, compensation, recruitment, and benefits (plus probably dozens of other areas). Each of these areas is complex and constantly changing. There is no way a manager could be an expert in all those areas. In fact, she may have been an expert at one point, but as soon as she became a manager her skills started to atrophy.
The Great Manager realizes this and entrusts the team to be the experts. It gives them autonomy and responsibility. It is hard - particularly since most managers think they are supposed to have all the answers.
Focus on ensuring that the people on the team are experts where they need to be, not on being seen as the expert.