CMS Energy Corporation is an energy company operating primarily in Michigan. The Company manages its businesses by the nature of services each provides, and operates principally in three segments: Electric Utility, Gas Utility, and NorthStar Clean Energy. The Electric Utility segment consisting of regulated activities associated with the generation, purchase, distribution, and sale of electricity in Michigan. The Gas Utility segment consisting of regulated activities associated with the purchase, transmission, storage, distribution, and sale of natural gas in Michigan. The NorthStar Clean Energy segment consisting of subsidiaries engaging in domestic independent power production, including the development and operation of renewable generation, and the marketing of independent power production. Its gas transmission, storage, and distribution system consist of over 2,380 miles of transmission lines with 15 gas storage fields with a total storage capacity of 309 billion cubic feet (bcf).