Equity, Capital and Other Interests Text (Details) (USD $)	3 Months Ended		9 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2012	Mar. 31, 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
Average Price Per Common Share Issued				$ 55.99	$ 54.75
Stock Issued During Period, Value, New Issues				$ 1,900,000,000	$ 1,200,000,000
Payments of Stock Issuance Costs	406,000	1,887,000			35,900,000
Units Issued During Period New Issues				34,468,085	21,850,000
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program	17,000,000
Common Shares Added To Atm Program	5,700,000
Additional Common Shares Authorized	6,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 464,600,000