Variable Interest Entities - Consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 338,742.2		$ 341,376.5
Total liabilities	326,465.3		328,985.2
Redeemable noncontrolling interest	426.6	$ 711.7	474.3	$ 410.1	$ 391.2	$ 337.7
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Total assets	43,187.5		44,585.2
Total liabilities	40,339.8		41,519.8
Redeemable noncontrolling interest	414.3		440.9
Mandatory retirement savings funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	40,583.9		41,865.2
Total liabilities	40,182.8		41,450.5
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	916.7		883.4
Total liabilities	22.6		34.2
Sponsored investment funds
Carrying amounts of consolidated VIE assets and liabilities
Total assets	823.1		851.4
Total liabilities	21.4		16.3
Redeemable noncontrolling interest	414.3		440.9
Residential mortgage loans VIE
Carrying amounts of consolidated VIE assets and liabilities
Total assets	666.3		728.9
Total liabilities	18.5		18.8
Collateralized loan obligations
Carrying amounts of consolidated VIE assets and liabilities
Total assets	114.3
Total liabilities	94.5
Asset-backed limited partnership
Carrying amounts of consolidated VIE assets and liabilities
Total assets	$ 83.2		$ 256.3