Consolidated Investment Products (CIP) - VIE Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	$ 429.6	$ 301.7	$ 289.0
Accounts receivable and other assets of CIP	258.4	175.5
Investments of CIP	7,912.1	7,910.0
Total assets	34,881.5	36,504.1
Debt of CIP	6,700.9	6,714.1
Other liabilities of CIP	663.6	588.6
Total liabilities	19,513.7	21,483.4
Total equity	15,029.5	14,808.9	13,942.4	$ 14,318.3
Total liabilities, temporary and permanent equity	34,881.5	36,504.1
VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	0.1		2.4
Accounts receivable and other assets of CIP	0.0		0.1
Investments of CIP	13.6		26.3
Total assets	13.7		28.8
Debt of CIP	0.0		2.0
Other liabilities of CIP	0.0		15.9
Total liabilities	0.0		17.9
Total equity	13.7		10.9
Total liabilities, temporary and permanent equity	13.7		28.8
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	0.0	0.0
Accounts receivable and other assets of CIP	1.0	0.0
Investments of CIP	131.4	0.0
Total assets	132.4	0.0
Debt of CIP	0.0	0.0
Other liabilities of CIP	1.0	0.0
Total liabilities	1.0	0.0
Total equity	131.4	0.0
Total liabilities, temporary and permanent equity	132.4	$ 0.0
Deconsolidated VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	6.1		0.1
Accounts receivable and other assets of CIP	1.8		2.9
Investments of CIP	284.4		127.3
Total assets	292.3		130.3
Debt of CIP	0.0		0.0
Other liabilities of CIP	17.3		1.5
Total liabilities	17.3		1.5
Total equity	275.0		128.8
Total liabilities, temporary and permanent equity	292.3		130.3
Deconsolidated Voes's
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	0.1		0.2
Accounts receivable and other assets of CIP	0.1		1.0
Investments of CIP	26.3		106.0
Total assets	26.5		107.2
Debt of CIP	0.0		0.0
Other liabilities of CIP	0.0		0.0
Total liabilities	0.0		0.0
Total equity	26.5		107.2
Total liabilities, temporary and permanent equity	$ 26.5		$ 107.2