Debt (Details) (USD $)	9 Months Ended
	Sep. 30, 2011 Year Project Apartment Property Store Customers OptionPlan State MilitaryHouse	Dec. 31, 2010
Debt Instrument [Line Items]
Mortgage notes payable	$ 4,136,848,000	$ 4,762,896,000
Interest rate range from minimum	0.74%
Interest rate range to maximum	7.57%
Average interest rate	1.32%
Unsecured debt, stated interest rate	6.95%
Maturity date description	October 5,2012
Unsecured revolving credit facility	1,250,000,000
Line of credit maturity	Feb. 28, 2012
Debt (Textuals) [Abstract]
Scheduled principal repayments	871,500,000
Write-off of unamortized deferred financing costs	4,100,000
Obtained new mortgage loans	152,900,000
Assumed mortgage debt	99,100,000
Properties acquired	3
Outstanding unsecured notes	4,600,000,000
Repayment of unsecured notes	93,100,000
Interest rate range from minimum	0.74%
Interest rate range to maximum	7.57%
Weighted average interest rate 5.16%	5.16%
Term loan facility amount	500,000,000
No of extension options	2
Period of extension options	1
Line of Credit Maturity	July 13, 2014
Advances under credit facility LIBOR plus spread	1.15%
Percentage of facility fee paid by the company	0.20%
Amount available on the credit facility	1,140,000,000
Amount restricted/dedicated to support letters of credit	85,900,000
Line of credit amount outstanding	26,000,000
Redeemed convertible unsecured notes	482,500,000
Redeemed convertible unsecured debt premium	0
500.0 million ability to increase	500,000,000
Unamortized deferred financing costs write-off	200,000
Various period of outstanding mortgage indebtedness	September 1,2048
Secured Debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	411,200,000
Company range of interest rates on outstanding mortgage indebtedness at various dates through September 1, 2048 [Member]
Debt Instrument [Line Items]
Interest rate range from minimum	0.14%
Interest rate range to maximum	11.25%
Average interest rate	4.83%
Debt (Textuals) [Abstract]
Interest rate range from minimum	0.14%
Interest rate range to maximum	11.25%
3.85% Unsecured Debt [Member]
Debt Instrument [Line Items]
Unsecured debt, stated interest rate	3.85%
Maturity date description	2026
Previous line of credit facility [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 1,425,000,000