Consolidated Investment Products (VIE Balance Sheets Consolidated In Period) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	$ 260.8	$ 511.3	$ 535.7
Accounts receivable and other assets of CIP	157.5	131.5
Investments of CIP	5,453.5	5,658.0
Total assets	31,619.1	31,668.8
Debt of CIP	4,502.7	4,799.8
Other liabilities of CIP	349.5	498.8
Total liabilities	22,148.1	22,470.0
Total equity	9,190.0	8,955.6	7,833.2	$ 7,611.8
Total liabilities and equity	31,619.1	$ 31,668.8
CLOs - VIEs [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	39.3		10.9
Accounts receivable and other assets of CIP	8.3		3.2
Investments of CIP	339.9		139.9
Total assets	387.5		154.0
Debt of CIP	375.3		0.0
Other liabilities of CIP	3.2		1.9
Total liabilities	378.5		1.9
Total equity	9.0		152.1
Total liabilities and equity	$ 387.5		154.0
VOEs [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP			0.0
Accounts receivable and other assets of CIP			0.2
Investments of CIP			49.8
Total assets			50.0
Debt of CIP			0.0
Other liabilities of CIP			0.0
Total liabilities			0.0
Total equity			50.0
Total liabilities and equity			50.0
Consolidated Entities [Member] | CLOs - VIEs [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP			8.2
Accounts receivable and other assets of CIP			1.3
Investments of CIP			45.8
Total assets			55.3
Debt of CIP			15.1
Other liabilities of CIP			13.7
Total liabilities			28.8
Total equity			26.5
Total liabilities and equity			$ 55.3