Consolidated Investment Products (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) voting_interest_entity variable_interest_entity	Mar. 31, 2015 variable_interest_entity	Dec. 31, 2015 USD ($)
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 244.0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	$ 244.0
VIEs invested in and consolidated, number of entities | variable_interest_entity	2	1
Voting Interest Entity, Initial Consolidation, Number of Entities | voting_interest_entity	1
Pay interest at Libor or Euribor plus	9.50%
Collateral assets, default percentage	0.20%		0.10%
Notes issued by collateralized loan obligations terms of arrangements interest rate margin spread low	0.21%
Notes issued by collateralized loan obligations terms of arrangements interest rate margin spread high	7.45%
CLO [Member]
Variable Interest Entity [Line Items]
Weighted average maturity (years)	9 years 8 months
Bank Loan Obligations [Member]
Variable Interest Entity [Line Items]
CLO Collateral Assets			$ 5,179.6
Senior Secured Bank Loans And Bonds [Member] | CLO [Member]
Variable Interest Entity [Line Items]
Fair value, option, aggregate differences, long-term debt instruments	$ 259.4		$ 319.9
Minimum [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Term	7 years
Maximum [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity Term	12 years
Consolidated Entities [Member] | Bank Loan Obligations [Member] | CLO [Member]
Variable Interest Entity [Line Items]
CLO Collateral Assets	$ 3,001.0