Real Estate and In-Place Lease Value - Joint Venture Consolidations (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Real Estate Properties [Line Items]
Cash	$ 38.5
Real estate and acquired in-place lease values, net	1,168.6
Accounts receivable and other assets	28.4
Accounts payable, accrued expenses, and other liabilities	23.0
Investment debt	574.0
Noncontrolling interests	353.3
Acquisition related gain	151.4
Multifamily Acquired in Ireland [Member]
Real Estate Properties [Line Items]
Cash	3.6
Real estate and acquired in-place lease values, net	248.5
Accounts receivable and other assets	0.9
Accounts payable, accrued expenses, and other liabilities	5.4
Investment debt	114.3
Noncontrolling interests	66.6
Acquisition related gain	39.3
Number of properties acquired	3
Commercial Acquired in Ireland [Member]
Real Estate Properties [Line Items]
Cash	4.3
Real estate and acquired in-place lease values, net	223.9
Accounts receivable and other assets	7.6
Accounts payable, accrued expenses, and other liabilities	4.9
Investment debt	75.2
Noncontrolling interests	77.9
Acquisition related gain	33.5
Number of properties acquired	2
Commercial and Loan Acquired in UK [Member]
Real Estate Properties [Line Items]
Cash	9.6
Real estate and acquired in-place lease values, net	195.0
Accounts receivable and other assets	5.6
Accounts payable, accrued expenses, and other liabilities	8.1
Investment debt	100.8
Noncontrolling interests	62.0
Acquisition related gain	11.9
Number of properties acquired	2
Multifamily Acquired in Japan [Member]
Real Estate Properties [Line Items]
Cash	21.0
Real estate and acquired in-place lease values, net	501.2
Accounts receivable and other assets	14.3
Accounts payable, accrued expenses, and other liabilities	4.6
Investment debt	283.7
Noncontrolling interests	146.8
Acquisition related gain	$ 66.7
Number of properties acquired	50