Business and Organization (Details) (USD $) In Billions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 segments decades
Business and Organization [Line Items]
Period over which the entity has made the investment across a range of real estate (in decades)	2
Number of primary business segments (in segments)	3
Minimum
Business and Organization [Line Items]
Investment across a range of real estate sectors over the past two decades	35