Equity, Capital and Other Interests Text (Details) (USD $)	6 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Aug. 08, 2013	Jun. 30, 2013 Archstone Transaction [Member]	Dec. 31, 2012 Public Offering [Member]
Stock Repurchased And Retired	0
Issuance of Common Shares	34,468,085			34,468,085	21,850,000
Stock Issued During Period, Value, New Issues				$ 1,900,000,000	$ 1,200,000,000
Average Price Per Common Share Issued				$ 55.99	$ 54.75
Units Issued During Period New Issues				34,468,085	21,850,000
Payments of Stock Issuance Costs	744,000	1,907,000			35,900,000
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program	17,000,000		13,000,000
Common Shares Added To Atm Program	5,687,478
Additional Common Shares Authorized	6,000,000		13,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 464,600,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			13,000,000