Consolidated Investment Products (Fair Value Hierarchy Levels Of Investments Held And Notes Issued By Consolidated Investment Products) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments Of Consolidated Investment Products	$ 5,658.0	$ 5,116.1
CLO notes	(22,470.0)	(17,838.8)
Real Estate Investments, Net	76.2	40.7
Investment in master fund		57.7
Fair Value, Inputs, Level 1 [Member]
Investments Of Consolidated Investment Products	217.8	179.0
Real Estate Investments, Net	0.0	0.0
Investment in master fund		0.0
Fair Value, Inputs, Level 2 [Member]
Investments Of Consolidated Investment Products	5,200.6	4,770.1
Real Estate Investments, Net	0.0	0.0
Investment in master fund		0.0
Significant Unobservable Inputs (Level 3) [Member]
Investments Of Consolidated Investment Products	76.2	40.7
Real Estate Investments, Net	76.2	40.7
Investment in master fund		0.0
Bank Loans [Member]
CLO Collateral Assets	4,894.2	4,397.8
Bank Loans [Member] | Fair Value, Inputs, Level 1 [Member]
CLO Collateral Assets	0.0	0.0
Bank Loans [Member] | Fair Value, Inputs, Level 2 [Member]
CLO Collateral Assets	4,894.2	4,397.8
Bank Loans [Member] | Significant Unobservable Inputs (Level 3) [Member]
CLO Collateral Assets	0.0	0.0
Bonds [Member]
CLO Collateral Assets	302.0	370.9
Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
CLO Collateral Assets	0.0	166.0
Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
CLO Collateral Assets	302.0	370.9
Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
CLO Collateral Assets	0.0	0.0
Equity Securities [Member]
CLO Collateral Assets	203.2	167.4
Private Equity Fund Assets	19.0	13.0
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
CLO Collateral Assets	198.8
Private Equity Fund Assets	19.0	13.0
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
CLO Collateral Assets	4.4	1.4
Private Equity Fund Assets	0.0	0.0
Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
CLO Collateral Assets	0.0
Private Equity Fund Assets	0.0	0.0
Private Equity Funds [Member]
Private Equity Fund Assets	163.4	68.6
Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Private Equity Fund Assets	0.0	0.0
Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Private Equity Fund Assets	0.0	0.0
Private Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Private Equity Fund Assets	0.0	0.0
Portion at Other than Fair Value Measurement [Member]
Investments Of Consolidated Investment Products	163.4	126.3
Real Estate Investments, Net	0.0	0.0
Investment in master fund		57.7
Portion at Other than Fair Value Measurement [Member] | Bank Loans [Member]
CLO Collateral Assets	0.0	0.0
Portion at Other than Fair Value Measurement [Member] | Bonds [Member]
CLO Collateral Assets	0.0	0.0
Portion at Other than Fair Value Measurement [Member] | Equity Securities [Member]
CLO Collateral Assets	0.0
Private Equity Fund Assets	0.0	0.0
Portion at Other than Fair Value Measurement [Member] | Private Equity Funds [Member]
Private Equity Fund Assets	$ 163.4	$ 68.6