Summary of Significant Accounting Policies - Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Consolidated VIEs, assets	$ 20,788.7	$ 15,644.8
Consolidated VIEs, liabilities	15,755.7	$ 12,714.6
Consolidated VIEs
Variable Interest Entity [Line Items]
Consolidated VIEs, assets	6,800.0
Consolidated VIEs, liabilities	6,600.0
Consolidated VIEs \| Collateralized Loan Obligations
Variable Interest Entity [Line Items]
Investments in CLOs	$ 172.8

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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+ Details

- Definition

Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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