Consolidated Investment Products (Investments Measured at NAV as a practical expedient) (Details) - Private Equity Funds [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Investment Owned, at Fair Value	$ 165.1	$ 163.4
Unfunded Commitments	$ 39.2	$ 53.9
Weighted Average Remaining Term	5 years 11 months	5 years 6 months