Unconsolidated Investments (Schedule of Joint Ventures) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 473.3	$ 751.4
Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	401.1	400.6
Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		68.8
United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	44.3	110.8
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		144.3
SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	27.9	26.9
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	134.3	250.3
Multifamily [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	134.3	133.3
Multifamily [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		68.8
Multifamily [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Multifamily [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		48.2
Multifamily [Member] | SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	201.7	360.9
Commercial [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	157.4	160.3
Commercial [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Commercial [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	44.3	104.5
Commercial [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		96.1
Commercial [Member] | SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Loan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	50.1	56.6
Loan [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	50.1	50.3
Loan [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Loan [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	6.3
Loan [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Loan [Member] | SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Residential [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	50.0	48.7
Residential [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	50.0	48.7
Residential [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Residential [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Residential [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Residential [Member] | SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Other [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	37.2	34.9
Other [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	9.3	8.0
Other [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Other [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Other [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures		0
Other [Member] | SPAIN
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 27.9	$ 26.9