Assets and Liabilities Measured at Fair Value on a Recurring Basis - Schedule of Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis, Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) included in changes in net assets	$ 23.8	$ 26.3
Loans Payable
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(830.3)	(1,585.5)
Total realized and unrealized gains (losses) included in changes in net assets	9.9	4.3
Purchases	0.0	0.0
Sales	0.0	0.0
Settlements	10.6	225.4
Ending balance	(809.8)	(1,355.8)
Line of Credit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(160.0)
Total realized and unrealized gains (losses) included in changes in net assets	0.0
Purchases	0.0
Sales	0.0
Settlements	0.0
Ending balance	(160.0)
Real Estate Properties
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	15,975.4	15,607.0
Total realized and unrealized gains (losses) included in changes in net assets	(63.4)	(76.2)
Purchases	299.2	186.3
Sales	(188.2)	(170.8)
Settlements	0.0	0.0
Ending balance	16,023.0	15,546.3
Real Estate Joint Ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5,098.8	5,381.4
Total realized and unrealized gains (losses) included in changes in net assets	(1.1)	90.6
Purchases	58.4	43.6
Sales	0.0	0.0
Settlements	(19.2)	(281.1)
Ending balance	5,136.9	5,234.5
Real Estate Operating Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,072.6	931.8
Total realized and unrealized gains (losses) included in changes in net assets	9.4	(0.2)
Purchases	0.0	127.2
Sales	0.0	0.0
Settlements	0.0	0.0
Ending balance	1,082.0	1,058.8
Loans Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	690.4	877.8
Total realized and unrealized gains (losses) included in changes in net assets	(0.6)	0.8
Purchases	3.3	2.1
Sales	0.0	0.0
Settlements	(128.8)	(28.1)
Ending balance	564.3	852.6
Total Level 3 Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	22,837.2	22,798.0
Total realized and unrealized gains (losses) included in changes in net assets	(55.7)	15.0
Purchases	360.9	359.2
Sales	(188.2)	(170.8)
Settlements	(148.0)	(309.2)
Ending balance	$ 22,806.2	$ 22,692.2

Assets and Liabilities Measured at Fair Value on a Recurring Basis - Schedule of Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis, Unobservable Inputs (Details) - USD ($)
$ in Millions

3 Months Ended

Mar. 31, 2026

Mar. 31, 2025

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]

Total realized and unrealized gains (losses) included in changes in net assets

$ 23.8

$ 26.3

Loans Payable

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]

Beginning balance

(830.3)

(1,585.5)