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
	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains included in changes in net assets	$ 1,389.2	$ 342.8
Loans Payable
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(2,380.5)	(2,411.4)
Total realized and unrealized gains included in changes in net assets	3.7	3.5
Purchases	(3.0)
Settlements	41.8	4.3
Ending balance	(2,338.0)	(2,403.6)
Line of Credit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(500.0)
Settlements	0.0
Ending balance	(500.0)
Real Estate Properties
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	18,903.9	16,476.7
Total realized and unrealized gains included in changes in net assets	1,204.0	290.8
Purchases	228.9	52.0
Sales	(157.7)	(3.0)
Ending balance	20,179.1	16,816.5
Real Estate Joint Ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7,175.9	6,128.9
Total realized and unrealized gains included in changes in net assets	122.8	54.3
Purchases	251.3	32.2
Settlements	(296.7)	(0.1)
Ending balance	7,253.3	6,215.3
Real Estate Operating Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	326.3	250.0
Total realized and unrealized gains included in changes in net assets	60.4
Purchases	100.9
Ending balance	487.6	250.0
Loans Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,492.6	1,562.5
Total realized and unrealized gains included in changes in net assets	1.0	12.6
Purchases	5.2	46.6
Sales	(161.4)	(81.2)
Settlements	(8.2)	(10.9)
Ending balance	1,329.2	1,529.6
Total Level 3 Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	27,898.7	24,418.1
Total realized and unrealized gains included in changes in net assets	1,388.2	357.7
Purchases	586.3	130.8
Sales	(319.1)	(84.2)
Settlements	(304.9)	(11.0)
Ending balance	$ 29,249.2	$ 24,811.4