Assets and Liabilities Measured at Fair Value on a Recurring Basis - Schedule of fair value assets and liabilities measured on recurring basis using unobservable inputs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized (losses) gains included in changes in net assets	$ 10.2	$ (524.6)	$ 36.5	$ (1,300.0)
Real Estate Properties
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	15,546.3	17,362.6	15,607.0	18,020.3
Total realized and unrealized (losses) gains included in changes in net assets	18.6	(403.2)	(57.6)	(984.6)
Purchases	392.6	63.1	578.9	145.3
Sales	(506.5)	(407.6)	(677.3)	(566.1)
Settlements	0.0	0.0	0.0	0.0
Ending balance	15,451.0	16,614.9	15,451.0	16,614.9
Real Estate Joint Ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5,234.5	5,748.8	5,381.4	5,881.2
Total realized and unrealized (losses) gains included in changes in net assets	(59.1)	(107.9)	31.5	(302.4)
Purchases	47.6	153.9	91.3	226.0
Sales	0.0	0.0	0.0	0.0
Settlements	(2.2)	(0.4)	(283.4)	(10.4)
Ending balance	5,220.8	5,794.4	5,220.8	5,794.4
Real Estate Operating Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,058.8	743.3	931.8	685.9
Total realized and unrealized (losses) gains included in changes in net assets	(27.8)	(12.8)	(28.0)	43.2
Purchases	2.1	0.0	129.3	1.4
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Ending balance	1,033.1	730.5	1,033.1	730.5
Loans Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	852.6	1,093.6	877.8	1,183.7
Total realized and unrealized (losses) gains included in changes in net assets	(7.4)	(19.2)	(6.6)	(113.8)
Purchases	4.2	3.4	6.3	9.3
Sales	0.0	0.0	0.0	0.0
Settlements	(0.3)	(0.5)	(28.4)	(1.9)
Ending balance	849.1	1,077.3	849.1	1,077.3
Total Level 3 Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	22,692.2	24,948.3	22,798.0	25,771.1
Total realized and unrealized (losses) gains included in changes in net assets	(75.7)	(543.1)	(60.7)	(1,357.6)
Purchases	446.5	220.4	805.8	382.0
Sales	(506.5)	(407.6)	(677.3)	(566.1)
Settlements	(2.5)	(0.9)	(311.8)	(12.3)
Ending balance	22,554.0	24,217.1	22,554.0	24,217.1
Loans Payable
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(1,355.8)	(1,870.1)	(1,585.5)	(1,862.5)
Total realized and unrealized (losses) gains included in changes in net assets	60.7	(9.1)	65.0	(17.9)
Purchases	0.0	(1.0)	0.0	(2.5)
Sales	0.0	0.0	0.0	0.0
Settlements	361.8	172.9	587.2	175.6
Ending balance	(933.3)	(1,707.3)	(933.3)	(1,707.3)
Line of Credit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0.0	(316.0)	0.0	(463.0)
Total realized and unrealized (losses) gains included in changes in net assets	0.0	0.0	0.0	0.0
Purchases	(219.0)	(90.0)	(219.0)	(121.0)
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	253.0	0.0	431.0
Ending balance	$ (219.0)	$ (153.0)	$ (219.0)	$ (153.0)

Assets and Liabilities Measured at Fair Value on a Recurring Basis - Schedule of fair value assets and liabilities measured on recurring basis using unobservable inputs (Details) - USD ($)
$ in Millions

3 Months Ended

6 Months Ended

Jun. 30, 2025

Jun. 30, 2024

Jun. 30, 2025

Jun. 30, 2024

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

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

$ 10.2

$ (524.6)

$ 36.5

$ (1,300.0)