Beijing is a global city and one of the world's leading centres for culture, diplomacy, politics, finance, business and economics, education, research, language, tourism, media, sport, science and technology and transportation. A megacity, Beijing is the second largest Chinese city by urban population after Shanghai and is the nation's cultural, educational, and political center.[17] It is home to the headquarters of most of China's largest state-owned companies and houses the largest number of Fortune Global 500 companies in the world, as well as the world's four biggest financial institutions by total assets.[18][19] Beijing is the "billionaire capital of the world" with the highest number of billionaires living in the city.[20][21] It is also a major hub for the national highway, expressway, railway, and high-speed rail networks. The Beijing Capital International Airport has been the second busiest in the world by passenger traffic (Asia's busiest) since 2010,[22] and, as of 2016, the city's subway network is the busiest and longest in the world. The Beijing Daxing International Airport, a second international airport in Beijing, is the largest single-structure airport terminal in the world.[23][24]