Equity, Capital and Other Interests Text (Details) (USD $)	6 Months Ended	9 Months Ended			12 Months Ended
	Jun. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Archstone Transaction [Member]	Dec. 31, 2012 Public Offering [Member]
Stock Repurchased and Retired During Period, Shares		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		954,000	2,860,000		35,900,000
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program		17,000,000
Common Shares Added To Atm Program		5,687,478
Additional Common Shares Authorized		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