CONSOLIDATED INVESTMENT PRODUCTS (CIP) - VIE Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	$ 536.3		$ 301.7	$ 254.0
Accounts receivable and other assets of CIP	273.7		175.5
Investments of CIP	8,924.2		7,910.0
Total assets	32,813.9		36,504.1
Debt of CIP	7,224.5		6,714.1
Other liabilities of CIP	864.9		588.6
Total liabilities	16,539.3		21,483.4
Total equity	15,732.0	$ 15,426.6	14,808.9	14,350.6	$ 13,967.7	$ 14,318.3
Total liabilities, temporary and permanent equity	32,813.9		$ 36,504.1
VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents of CIP	38.5			9.1
Accounts receivable and other assets of CIP	6.3			1.2
Investments of CIP	492.3			114.2
Total assets	537.1			124.5
Debt of CIP	136.1			23.9
Other liabilities of CIP	206.6			89.7
Total liabilities	342.7			113.6
Total equity	194.4			10.9
Total liabilities, temporary and permanent equity	537.1			124.5
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			0.4
Accounts receivable and other assets of CIP	1.8			2.8
Investments of CIP	284.4			216.9
Total assets	292.3			220.1
Debt of CIP	258.3			0.0
Other liabilities of CIP	17.3			2.0
Total liabilities	275.6			2.0
Total equity	16.7			218.1
Total liabilities, temporary and permanent equity	292.3			220.1
Deconsolidated 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			1.1
Investments of CIP	27.6			134.1
Total assets	27.8			135.4
Debt of CIP	0.0			0.0
Other liabilities of CIP	0.0			0.0
Total liabilities	0.0			0.0
Total equity	27.8			135.4
Total liabilities, temporary and permanent equity	$ 27.8			$ 135.4