Fair Value Measurements - Fair Value Option on Consolidated VIEs and Equity Method Investments (Details) - Real Estate Ventures - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value Option, Quantitative Disclosures
Fair value of assets for which fair value option was elected					$ 28.5
Pre-tax gain (loss) due to change in fair value of assets and liabilities for which the fair value option was elected	$ (0.1)	$ 1.7	$ 12.6	$ 4.0

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123596393&loc=d3e14172-108612

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration