Unconsolidated Investees (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Summarized financial information of the property fund entities
Revenues	$ 1,567.4	$ 1,515.6
Net earnings (loss)	49.3	(81.2)
Total assets	20,692.9	16,386.2
Amounts due to us	76.9	30.6
Third party debt	9,290.0	7,722.2
Total liabilities	10,319.3	8,714.4
Noncontrolling interest	7.9	5.9
Fund partners' equity	10,365.7	7,665.9
Our weighted average ownership	27.90%	29.80%
Our investment balance	2,471.2	1,890.0
Deferred gains, net of amortization	418.7	532.2
Europe [Member]
Summarized financial information of the property fund entities
Revenues	600.1	723.3
Net earnings (loss)	73.6	48.3
Total assets	6,211.8	8,176.7
Amounts due to us	8.1	(5.9)
Third party debt	2,275.8	3,476.8
Total liabilities	2,758.9	4,131.7
Noncontrolling interest	6.2	5.9
Fund partners' equity	3,446.7	4,039.1
Our weighted average ownership	29.90%	31.30%
Our investment balance	662.0	936.9
Deferred gains, net of amortization	191.0	297.1
Asia [Member]
Summarized financial information of the property fund entities
Revenues	95.5	11.4
Net earnings (loss)	(0.5)	(21.2)
Total assets	2,245.1	127.3
Amounts due to us	9.3	0.2
Third party debt	1,061.4	49.2
Total liabilities	1,174.0	52.9
Noncontrolling interest	0	0
Fund partners' equity	1,071.1	74.4
Our weighted average ownership	19.40%	20.00%
Our investment balance	212.9	16.7
Deferred gains, net of amortization	0.1	0
Americas [Member]
Summarized financial information of the property fund entities
Revenues	871.8	780.9
Net earnings (loss)	(23.8)	(108.3)
Total assets	(12,236.0)	8,082.2
Amounts due to us	59.5	36.3
Third party debt	5,952.8	4,196.2
Total liabilities	6,386.4	4,529.8
Noncontrolling interest	(1.7)	0
Fund partners' equity	5,847.9	3,552.4
Our weighted average ownership	28.20%	28.50%
Our investment balance	1,596.3	936.4
Deferred gains, net of amortization	$ 227.6	$ 235.1