REVENUE RECOGNITION - Additional disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Customer Frequency Program
Deferred revenues and income	$ 405.4	$ 449.2
Gift Card And Ticket Exchange
Customer Frequency Program
Redemption period	24 months
Deferred revenues and income	$ 319.7
Loyalty Program
Customer Frequency Program
Redemption period	24 months
Deferred revenues and income	$ 67.0
Exhibitor Services Agreement
Customer Frequency Program
Expected to be recognized as revenue	537.6
Exhibitor Services Agreement \| Year Ended 2021
Customer Frequency Program
Expected to be recognized as revenue	18.1
Exhibitor Services Agreement \| Year Ended 2022
Customer Frequency Program
Expected to be recognized as revenue	19.5
Exhibitor Services Agreement \| Year Ended 2023
Customer Frequency Program
Expected to be recognized as revenue	21.0
Exhibitor Services Agreement \| Year Ended 2024
Customer Frequency Program
Expected to be recognized as revenue	22.6
Exhibitor Services Agreement \| Year Ended 2025
Customer Frequency Program
Expected to be recognized as revenue	24.3
Exhibitor Services Agreement \| Years Ended 2026 through February 2037
Customer Frequency Program
Expected to be recognized as revenue	$ 432.1