Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 334,491.8		$ 313,663.6
Total liabilities	322,363.8		302,194.6
Redeemable noncontrolling interest	410.1	$ 391.2	337.7	$ 311.8	$ 277.4	$ 248.9
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	41,361.6		35,834.9
Total liabilities	38,378.1		33,051.8
Redeemable noncontrolling interest	381.3		309.9
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	38,683.4		33,130.4
Total liabilities	38,300.6		32,802.2
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	865.6		814.3
Total liabilities	36.4		69.4
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	809.7		833.7
Total liabilities	22.2		160.3
Redeemable noncontrolling interest	381.3		309.9
Residential mortgage loans VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	748.5		806.5
Total liabilities	18.9		19.9
Asset-backed limited partnership
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 254.4		$ 250.0