Subsequent Events/Other (Details) (USD $) Share data in Millions, unless otherwise specified	0 Months Ended	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended	45 Months Ended
	Oct. 04, 2013	Nov. 08, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013
Subsequent Event [Line Items]
Proceeds from Issuance of Long-term Debt		$ 896,900,000				$ 5,951,000	$ 0
Debt Instrument, Maturity Date		Nov. 01, 2014				Sep. 01, 2014
Secured Debt			6,230,675,000	3,898,369,000		6,230,675,000		3,898,369,000	6,230,675,000
Repayments Of Mortgage Notes Payable		963,500,000				9,527,000	11,022,000
Noncash or Part Noncash Acquisition, Debt Assumed						34,100,000
Debt Instrument, Interest Rate, Stated Percentage		5.88%
Proceeds from Sale of Available-for-sale Securities	(300,000)	1,700,000				(828,000)	0
(Gain) Loss on Sale of Securities, Net		1,300,000	830,000		0	830,000	0
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program			17.0			17.0			17.0
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			13.0			13.0			13.0
Business Combination, Acquisition Related Costs						200,000	6,900,000		95,400,000
Noncash Project Abandonment Costs						3,969,000	6,141,000
Other Nonoperating Expense			3,986,000		3,984,000	7,530,000	18,587,000
Settlement Expense							4,200,000
Break Up Fee				80,000,000	70,000,000			150,000,000
Archstone [Member]
Subsequent Event [Line Items]
Secured Debt			2,000,000,000			2,000,000,000			2,000,000,000
Noncash or Part Noncash Acquisition, Debt Assumed						3,100,000,000
Other Expense [Member]
Subsequent Event [Line Items]
Other Nonoperating Expense						4,200,000	13,000,000
New York Life Loan [Member]
Subsequent Event [Line Items]
Proceeds from Issuance of Long-term Debt		800,000,000
Debt Instrument, Maturity Date		Nov. 10, 2023
Debt Instrument, Interest Rate, Stated Percentage		4.21%
Archstone Transaction [Member]
Subsequent Event [Line Items]
Debt Instrument, Maturity Date		Nov. 01, 2017
Secured Debt		440,000,000
Repayments Of Mortgage Notes Payable		825,000,000
Noncash or Part Noncash Acquisition, Debt Assumed						$ 1,270,000,000
Debt Instrument, Interest Rate, Stated Percentage		6.26%