Investments in Real Estate Funds (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Carrying Amount	$ 28,928.2	$ 25,937.8
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying Amount	648.0
Maximum Exposure to Loss	$ 648.0
Variable Interest Entity, Not Primary Beneficiary | LCS SHIP Venture I, LLC
Variable Interest Entity [Line Items]
Account Interest	90.00%
Carrying Amount	$ 227.8
Maximum Exposure to Loss	$ 227.8
Variable Interest Entity, Not Primary Beneficiary | Veritas Trophy VI, LLC
Variable Interest Entity [Line Items]
Account Interest	90.40%
Carrying Amount	$ 60.8
Maximum Exposure to Loss	$ 60.8
Variable Interest Entity, Not Primary Beneficiary | SP V - II, LLC
Variable Interest Entity [Line Items]
Account Interest	61.80%
Carrying Amount	$ 76.8
Maximum Exposure to Loss	$ 76.8
Variable Interest Entity, Not Primary Beneficiary | Taconic New York City GP Fund, LP
Variable Interest Entity [Line Items]
Account Interest	60.00%
Carrying Amount	$ 30.0
Maximum Exposure to Loss	$ 30.0
Variable Interest Entity, Not Primary Beneficiary | Silverpeak NRE FundCo LLC
Variable Interest Entity [Line Items]
Account Interest	90.00%
Carrying Amount	$ 51.2
Maximum Exposure to Loss	$ 51.2
Variable Interest Entity, Not Primary Beneficiary | IDR - Core Property Index Fund, LLC
Variable Interest Entity [Line Items]
Account Interest	2.70%
Carrying Amount	$ 36.1
Maximum Exposure to Loss	$ 36.1
Variable Interest Entity, Not Primary Beneficiary | Townsend Group Value-Add Fund
Variable Interest Entity [Line Items]
Account Interest	99.00%
Carrying Amount	$ 51.8
Maximum Exposure to Loss	$ 51.8
Variable Interest Entity, Not Primary Beneficiary | Flagler - REA Healthcare Properties Partnership
Variable Interest Entity [Line Items]
Account Interest	90.00%
Carrying Amount	$ 22.7
Maximum Exposure to Loss	$ 22.7
Variable Interest Entity, Not Primary Beneficiary | Grubb Southeast Real Estate Fund VI, LLC
Variable Interest Entity [Line Items]
Account Interest	66.70%
Carrying Amount	$ 34.9
Maximum Exposure to Loss	$ 34.9
Variable Interest Entity, Not Primary Beneficiary | Silverpeak NRE FundCo 2 LLC
Variable Interest Entity [Line Items]
Account Interest	90.00%
Carrying Amount	$ 41.7
Maximum Exposure to Loss	$ 41.7
Variable Interest Entity, Not Primary Beneficiary | JCR Capital - REA Preferred Equity Parallel Fund
Variable Interest Entity [Line Items]
Account Interest	39.70%
Carrying Amount	$ 14.2
Maximum Exposure to Loss	$ 14.2