Consolidated Investment Products (VIE Balance Sheets Consolidated In Period) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	$ 301.7	$ 652.2	$ 657.7
Accounts receivable and other assets of CIP	175.5	172.9
Investments of CIP	7,910.0	7,808.0
Total assets	36,504.1	39,420.3
Debt of CIP	6,714.1	6,234.6
Other liabilities of CIP	588.6	949.6
Total liabilities	21,483.4	24,718.5
Total equity	14,808.9	14,318.3	$ 8,936.2	$ 8,955.6
Total liabilities, temporary and permanent equity	36,504.1	39,420.3
Consolidated VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	9.1	9.8
Accounts receivable and other assets of CIP	1.2	3.1
Investments of CIP	114.2	508.7
Total assets	124.5	521.6
Debt of CIP	75.8	188.8
Other liabilities of CIP	37.8	332.8
Total liabilities	113.6	521.6
Total equity	10.9	0.0
Total liabilities, temporary and permanent equity	124.5	521.6
Consolidated VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	0.1	0.2
Accounts receivable and other assets of CIP	0.1	0.3
Investments of CIP	17.1	25.5
Total assets	17.3	26.0
Debt of CIP	0.0	0.0
Other liabilities of CIP	0.0	0.0
Total liabilities	0.0	0.0
Total equity	17.3	26.0
Total liabilities, temporary and permanent equity	17.3	26.0
Deconsolidated VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	0.2	0.0
Accounts receivable and other assets of CIP	1.1	0.6
Investments of CIP	134.1	94.3
Total assets	135.4	94.9
Debt of CIP	0.0	0.0
Other liabilities of CIP	0.0	0.0
Total liabilities	0.0	0.0
Total equity	135.4	94.9
Total liabilities, temporary and permanent equity	135.4	94.9
Deconsolidated VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	4.0	7.6
Accounts receivable and other assets of CIP	5.0	22.3
Investments of CIP	373.7	626.1
Total assets	382.7	656.0
Debt of CIP	0.0	526.2
Other liabilities of CIP	2.8	22.2
Total liabilities	2.8	548.4
Total equity	379.9	107.6
Total liabilities, temporary and permanent equity	$ 382.7	$ 656.0