Concentration Risk - Voluntary Fee Waivers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Risks and Uncertainties [Abstract]
Revenue	$ 0.0	$ (4.4)	$ (87.8)
Less: Reduction in Distribution Expense	0.0	3.6	65.8
Operating Income	0.0	(0.8)	(22.0)
Less: Reduction in Noncontrolling Interest	0.0	0.0	0.0
Pre-tax Impact	$ 0.0	$ (0.8)	$ (22.0)