Variable Interest Entities (Non-Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	$ 462.8	$ 389.2
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	7.6	0.2
Maximum Exposure to Loss	1,211.9	1,461.1
Total VIE Assets	10,943.1	12,516.0
Collateralized Loan Obligations [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	74.7	73.6
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	7.6	0.2
Maximum Exposure to Loss	336.7	458.1
Total VIE Assets	4,900.2	6,368.7
Consumer Loan Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	170.0	188.3
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	607.2	845.8
Total VIE Assets	1,231.4	1,133.0
Related Party Private Equity Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	38.3	39.3
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	64.2	65.8
Total VIE Assets	157.5	168.2
Real Estate Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	89.9
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0
Maximum Exposure to Loss	101.4
Total VIE Assets	84.6
Other Private Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	89.9	88.0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	102.4	91.4
Total VIE Assets	$ 4,569.4	$ 4,846.1