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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
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	$ 99.5	$ 984.2	$ 2,791.5	$ 1,967.5
Loans Payable
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(2,293.0)	(2,388.2)	(2,380.5)	(2,411.4)
Total realized and unrealized gains (losses) included in changes in net assets	12.1	(3.0)	61.9	11.0
Purchases	(11.0)	(39.7)	(20.1)	(39.7)
Sales	0.0	0.0	0.0	0.0
Settlements	166.9	87.7	213.7	96.9
Ending balance	(2,125.0)	(2,343.2)	(2,125.0)	(2,343.2)
Line of Credit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(500.0)		(500.0)
Total realized and unrealized gains (losses) included in changes in net assets	0.0		0.0
Purchases	0.0		0.0
Sales	0.0		0.0
Settlements	500.0		500.0
Ending balance	0.0		0.0
Other Unsecured Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0.0		0.0
Total realized and unrealized gains (losses) included in changes in net assets	0.0		0.0
Purchases	(500.0)		(500.0)
Sales	0.0		0.0
Settlements	0.0		0.0
Ending balance	(500.0)		(500.0)
Real Estate Properties
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	21,288.6	17,029.8	18,903.9	16,476.7
Total realized and unrealized gains (losses) included in changes in net assets	99.1	530.9	2,280.7	1,425.7
Purchases	188.8	112.8	725.9	332.6
Sales	(86.3)	(274.8)	(420.3)	(836.3)
Settlements	0.0	0.0	0.0	0.0
Ending balance	21,490.2	17,398.7	21,490.2	17,398.7
Real Estate Joint Ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7,642.9	6,482.6	7,175.9	6,128.9
Total realized and unrealized gains (losses) included in changes in net assets	39.2	425.1	401.3	579.2
Purchases	97.4	180.5	579.1	380.4
Sales	0.0	0.0	0.0	0.0
Settlements	(420.2)	(35.1)	(797.0)	(35.4)
Ending balance	7,359.3	7,053.1	7,359.3	7,053.1
Real Estate Operating Business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	628.0	273.5	326.3	250.0
Total realized and unrealized gains (losses) included in changes in net assets	13.3	12.5	214.1	34.6
Purchases	0.8	0.0	101.7	1.4
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Ending balance	642.1	286.0	642.1	286.0
Loans Receivable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,558.1	1,391.8	1,492.6	1,562.6
Total realized and unrealized gains (losses) included in changes in net assets	(16.3)	1.5	(98.5)	6.1
Purchases	26.4	92.7	343.9	256.4
Sales	0.0	0.0	(161.4)	(294.5)
Settlements	(19.7)	(37.9)	(28.1)	(82.5)
Ending balance	1,548.5	1,448.1	1,548.5	1,448.1
Total Level 3 Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	31,117.6	25,177.7	27,898.7	24,418.2
Total realized and unrealized gains (losses) included in changes in net assets	135.3	970.0	2,797.6	2,045.6
Purchases	313.4	386.0	1,750.6	970.8
Sales	(86.3)	(274.8)	(581.7)	(1,130.8)
Settlements	(439.9)	(73.0)	(825.1)	(117.9)
Ending balance	$ 31,040.1	$ 26,185.9	$ 31,040.1	$ 26,185.9