Variable Interest Entities (Non-Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	$ 414.1	$ 566.9
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	1.5	4.8
Maximum Exposure to Loss	1,072.0	1,410.8
Total VIE Assets	9,530.3	10,229.3
CLOs [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	37.7	264.7
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	1.5	4.8
Maximum Exposure to Loss	285.7	930.0
Total VIE Assets	3,279.9	4,472.9
Consumer Loan Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	154.1	90.3
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	515.4	219.6
Total VIE Assets	1,149.1	985.5
Related Party Private Equity Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	36.3	37.6
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	62.0	63.6
Total VIE Assets	149.3	155.6
Real Estate Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	100.4	90.3
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	112.2	101.8
Total VIE Assets	111.3	85.6
Other Private Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Total Financial Statement Carrying Amount, Assets	85.6	84.0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0.0	0.0
Maximum Exposure to Loss	96.7	95.8
Total VIE Assets	$ 4,840.7	$ 4,529.7