Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 298,908.4		$ 296,627.7
Total liabilities	282,435.9		279,754.8
Redeemable noncontrolling interest	343.3	$ 330.6	255.6	$ 278.5	$ 272.7	$ 264.9
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	37,715.4		43,233.5
Total liabilities	34,848.1		41,552.4
Redeemable noncontrolling interest	309.7		226.8
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	35,161.0		41,995.2
Total liabilities	34,771.0		41,527.9
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	691.0		499.0
Total liabilities	42.8		21.3
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	525.9		419.5
Total liabilities	13.3		3.2
Redeemable noncontrolling interest	309.7		226.8
Residential mortgage loans VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	1,337.5		$ 319.8
Total liabilities	$ 21.0