CONSOLIDATED STATEMENTS OF ASSETS AND LIABILITIES (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Securities loaned	$ 2.4	$ 25.2
Cash collateral for securities loaned	2.5	25.7
Real estate properties at cost	14,098.9	13,048.5
Real estate joint ventures and funds at cost	5,042.0	6,244.4
Real estate-related Marketable securities at cost	800.4	686.0
Other Marketable securities at cost	1,354.4	4,144.7
Loans receivable at cost	1,574.5	1,504.5
Loans receivable from related parties at cost	69.3	69.3
Cost of Total investments	22,939.5	25,697.4
Principal outstanding on loans payable	$ 2,624.3	$ 2,338.0