REVENUE - Market Fee Waivers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue, Major Customer [Line Items]
Reduction in investment management and service and distribution fees, gross	$ (1,750.0)	$ (1,497.6)	$ (5,131.1)	$ (4,515.5)
Investment management and Services and distribution fees
Revenue, Major Customer [Line Items]
Reduction in investment management and service and distribution fees, gross	$ 40.8	$ 12.4	$ 111.2	$ 23.1