Unconsolidated Investments (Schedule of Joint Ventures) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 584.5	$ 751.4
Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	405.5	400.6
Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	67.9	68.8
United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	51.0	110.8
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	33.3	144.3
Spain [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	26.8	26.9
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	204.8	250.3
Multifamily [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	136.9	133.3
Multifamily [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	67.9	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	0	48.2
Multifamily [Member] | Spain [Member]
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	243.5	360.9
Commercial [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	159.2	160.3
Commercial [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	0
Commercial [Member] | United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	51.0	104.5
Commercial [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	33.3	96.1
Commercial [Member] | Spain [Member]
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	50.7	56.6
Loan [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	50.7	50.3
Loan [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	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	0
Loan [Member] | Spain [Member]
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	49.0	48.7
Residential [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	49.0	48.7
Residential [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	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	0
Residential [Member] | Spain [Member]
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	36.5	34.9
Other [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	9.7	8.0
Other [Member] | Japan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0	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	0
Other [Member] | Spain [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 26.8	$ 26.9