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		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
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	$ (244.6)	$ (821.6)	$ (1,544.6)	$ (3,189.5)
Real Estate Properties
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	16,614.9	19,191.3	18,020.3	20,444.0
Total realized and unrealized (losses) gains included in changes in net assets	(170.2)	(464.7)	(1,154.8)	(1,897.5)
Purchases	108.0	75.7	253.2	255.8
Sales	(328.9)		(894.9)
Settlements	0.0	0.0	0.0	0.0
Ending balance	16,223.8	18,802.3	16,223.8	18,802.3
Real Estate Joint Ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5,794.4	6,341.5	5,881.2	7,103.6
Total realized and unrealized (losses) gains included in changes in net assets	(154.5)	(278.1)	(456.9)	(1,006.3)
Purchases	85.2	88.2	311.2	179.6
Sales	0.0		0.0
Settlements	0.0	(0.2)	(10.4)	(125.5)
Ending balance	5,725.1	6,151.4	5,725.1	6,151.4
Real Estate Operating Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	730.5	653.6	685.9	641.9
Total realized and unrealized (losses) gains included in changes in net assets	97.2	(3.5)	140.4	(8.2)
Purchases	69.9	0.0	71.3	16.4
Sales	0.0		0.0
Settlements	0.0	0.0	0.0	0.0
Ending balance	897.6	650.1	897.6	650.1
Loans Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,077.3	1,365.5	1,183.7	1,488.6
Total realized and unrealized (losses) gains included in changes in net assets	(46.1)	(62.3)	(159.9)	(221.6)
Purchases	23.8	2.7	33.1	50.3
Sales	0.0		0.0
Settlements	(33.3)	(0.2)	(35.2)	(11.6)
Ending balance	1,021.7	1,305.7	1,021.7	1,305.7
Total Level 3 Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	24,217.1	27,551.9	25,771.1	29,678.1
Total realized and unrealized (losses) gains included in changes in net assets	(273.6)	(808.6)	(1,631.2)	(3,133.6)
Purchases	286.9	166.6	668.8	502.1
Sales	(328.9)		(894.9)
Settlements	(33.3)	(0.4)	(45.6)	(137.1)
Ending balance	23,868.2	26,909.5	23,868.2	26,909.5
Loans Payable
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(1,707.3)	(1,847.3)	(1,862.5)	(2,069.7)
Total realized and unrealized (losses) gains included in changes in net assets	3.7	(16.3)	(14.2)	(39.0)
Purchases	(58.3)	(213.5)	(60.9)	(313.6)
Sales	0.0		0.0
Settlements	20.3	214.5	196.0	559.7
Ending balance	(1,741.6)	(1,862.6)	(1,741.6)	(1,862.6)
Line of Credit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(153.0)	0.0	(463.0)	0.0
Total realized and unrealized (losses) gains included in changes in net assets	0.0	0.0	0.0	0.0
Purchases	(72.0)	(574.0)	(193.0)	(574.0)
Sales	0.0		0.0
Settlements	153.0	64.0	584.0	64.0
Ending balance	$ (72.0)	(510.0)	$ (72.0)	(510.0)
Other Unsecured Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		(500.0)		(500.0)
Total realized and unrealized (losses) gains included in changes in net assets		0.0		0.0
Purchases		0.0		0.0
Settlements		500.0		500.0
Ending balance		$ 0.0		$ 0.0