What is the fine-grained topic of the following text: National Fuel Gas Company (NYSE: NFG) is a diversified energy company with $6.2 billion in assets distributed among the following five operating segments: Exploration and Production (Seneca Resources Corporation), Pipeline and Storage, Gathering, Utility, and Energy Marketing (National Fuel Resources, Inc. - NFR). Only return the topic.
National Fuel Gas Company's Business Structure and Operations