Commitments And Contingencies (Details) $ in Millions		3 Months Ended	12 Months Ended
	Oct. 18, 2018 USD ($)	Jun. 30, 2020 fund	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Undrawn capital and purchase commitments			$ 453.5	$ 357.0
Authorized amount under common stock buyback program	$ 1,200.0
Stock repurchase program period in force	2 years
Seed Capital Subject to Massmutual Redemption Agreement
Loss Contingencies [Line Items]
Total amount of seed capital subject to the agreement			357.8
OppenheimerFunds Acquisition-related Matter
Loss Contingencies [Line Items]
Estimated liability			387.8
Adjustment to the initial acquisition liability			380.5
Liability recognized for activity after acquisition			7.3
Remediation costs			11.6
Rebalancing Correction Matter
Loss Contingencies [Line Items]
Number of funds with errors discovered and corrected | fund		2
Compensation payment made for the performance difference			$ 105.3