Question: Northern States Power Company is now a subsidiary of what utility holding company based in Minneapolis, Minnesota?
Context: Xcel Energy Inc. is a utility holding company based in Minneapolis, Minnesota, serving more than 3.3 million electric customers and 1.8 million natural gas customers in Minnesota, Michigan, Wisconsin, North Dakota, South Dakota, Colorado, Texas and New Mexico.  It consists of four operating subsidiaries: Northern States Power-Minnesota, Northern States Power-Wisconsin, Public Service Company of Colorado, and Southwestern Public Service Co. The North American Light and Power Company was a utility holding company formed in South Bend, Indiana and run since 1916 by its President, Clement Studebaker, Jr., of the family famous for the Studebaker automobiles.  The utility company remained a major subsidiary of the North American Company, until that conglomerate's 1940s breakup by the U.S. Securities and Exchange Commission (SEC). North American Co. v. Securities and Exchange Commission, 327 U.S. 686 (1946), is a United States Supreme Court case holding that a Securities and Exchange Commission (SEC) order under the Public Utility Holding Company Act (PUHCA) directing a public utility holding company to divest its securities of all companies except for one electric company did not violate the Commerce Clause or the Fifth Amendment to the United States Constitution. TECO Energy Inc. is an energy-related holding company based in Tampa, Florida, providing electricity to the greater Tampa area and central Florida, and natural gas throughout the state of Florida through its subsidiaries Tampa Electric Company and Peoples Gas Company respectively.  Another subsidiary, TECO Services, Inc., provides IT, HR, legal, facilities, and other common services to Tampa Electric, Peoples Gas, and former TECO subsidiary New Mexico Gas Company.  On September 4, 2015, Emera, a utility holding company based in Halifax, Nova Scotia, Canada, announced the pending acquisition of TECO Energy.  That purchase closed on July 1, 2016, and TECO Energy, Inc. is now a wholly owned subsidiary of Emera, Inc. Spire Inc. () is a public utility holding company based in St. Louis, Missouri, providing natural gas service through its regulated core utility operations while engaging in non-regulated activities that provide business opportunities.  Its primary subsidiary Laclede Gas Company is the largest natural gas distribution utility in Missouri, serving approximately 631,000 residential, commercial and industrial customers in the City of St. Louis and ten counties in eastern Missouri.  Its corporate headquarters is located in the 700 Market building in downtown St. Louis. Nuclear Management Company was a contract/operations firm that operated six nuclear power plants in the midwest US.  NMC provided operational collaborations between plants.  NMC did not own the plants, nor the energy produced from them.  NMC's corporate headquarters were in Hudson, Wisconsin.  As of September 2008 the operating licenses for the last two plants overseen by NMC, Monticello and Prairie Island, were transferred to Northern States Power Company (a wholly owned subsidiary of Xcel Energy), the owner of the plants.  All personnel and assets of NMC were transferred to NSP, rendering NMC defunct. The Ashland/Northern States Power Lakefront Superfund site is a contaminated region of the Wisconsin shoreline of Lake Superior that is being studied for remediation by Northern States Power Wisconsin (NSPW), as well as the Environmental Protection Agency (EPA), the Wisconsin Department of Natural Resources (WDNR).  This site has held a manufactured gas plant from 1845 to 1947, as well as lumber manufacturing and treatment mills for four decades at the start of the 20th century, railcar loading facilities, and a municipal landfill.  Additionally, a wastewater treatment plant is located on the premises, but is not in operation.  Contamination of the site is currently believed to have been caused by all the parties mentioned above, or former owners of the property whose companies are no longer in business.  The area is listed as a Superfund site by the EPA under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).  Releases of hazardous substances occurred onshore and migrated into sediment in Chequamagon Bay on Lake Superior. Northern States Power Company (NYSE: NSP ) was a publicly traded S&P 500 electric and natural gas utility holding company based in Minneapolis, Minnesota that is now a subsidiary of Xcel Energy (). Southern Company is an American gas and electric utility holding company based in the southern United States.  It is headquartered in Atlanta, Georgia, with executive offices also located in Birmingham, Alabama.  The company is currently the second largest utility company in the U.S., in terms of customer base.  Through its subsidiaries it serves 9 million gas and electric utility customers in nine states.  Southern Company’s regulated regional electric utilities serve a 120000 sqmi territory with 27000 mi of distribution lines. The Pathfinder Atomic Power Plant was a nuclear power plant built by Northern States Power Company.  It was located just northeast of Sioux Falls, South Dakota, and west of its suburb of Brandon.  It was named for the 19th century explorer John C. "Pathfinder" Fremont and was constructed in the mid-1960s in partnership with a group of other investor-owned utilities.  The main goal of this facility was to be a 'proof of concept' plant to gain practical experience in operating a nuclear plant.  Some of the other participating utilities would also go on to build their own plants.  Although the superheater developed by Allis-Chalmers was plagued with technical difficulties and which led to NSP's eventual decision to retire the reactor by 1967 (and convert the plant to run on gas and oil by 1968), the lessons NSP learned from Pathfinder served the company in its operation of the Prairie Island and Monticello nuclear plants.  The longest Pathfinder ever ran at its full rated power was 30 minutes, and it was only then the company found the flaws that led to the decision to retire the reactor.  After sitting idle for 23 years, the reactor vessel was removed from the plant in 1990 and transported to a low-level radioactive material dump in Washington.
Answer: Xcel Energy