Real Estate Archstone Acquisition (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) property shares	Dec. 31, 2014 USD ($) property shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2012 USD ($) $ / shares shares	Feb. 27, 2013 USD ($)
Properties acquired | property	4	6
Property Units Acquired	625	1,353
Master Leased Properties Acquired	3
Payments to Acquire Businesses, Net of Cash Acquired	$ 0	$ 0	$ 4,000,875,000
Secured Debt	$ 4,704,870,000	$ 5,086,515,000
Stock Issued During Period, Shares, New Issues | shares	0	0	34,468,085
Number Of Operating Properties Under Long Term Ground Leases	14
Land	$ 5,864,046,000	$ 6,295,404,000
Depreciable property Abstract
Buildings and improvements	16,336,829,000	17,974,337,000
Furniture, fixtures and equipment	1,207,098,000	1,365,276,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases	483,160,000	511,891,000
Projects under development	1,122,376,000	1,343,919,000
Land held for development	168,843,000	184,556,000
Other assets	422,027,000	383,754,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(366,387,000)	(389,915,000)
Business Combination, Acquisition Related Costs	1,000,000	400,000	$ 300,000
Payments of Financing Costs	6,425,000	10,982,000	16,526,000
Income (Loss) from Equity Method Investments	(15,025,000)	7,952,000	58,156,000
ERPOP [Member]
Payments to Acquire Businesses, Net of Cash Acquired	0	0	4,000,875,000
Secured Debt	4,704,870,000	5,086,515,000
Land	5,864,046,000	6,295,404,000
Depreciable property Abstract
Projects under development	1,122,376,000	1,343,919,000
Land held for development	168,843,000	184,556,000
Other assets	422,027,000	383,754,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(366,387,000)	(389,915,000)
Payments of Financing Costs	6,425,000	10,982,000	16,526,000
Income (Loss) from Equity Method Investments	(15,025,000)	7,952,000	$ 58,156,000
Consolidated Properties [Member]
Secured Debt	343,429,000
Depreciable property Abstract
Other assets	26,567,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(786,000)
Income (Loss) from Equity Method Investments	1,501,000
Unconsolidated Properties [Member]
Secured Debt	174,846,000
Depreciable property Abstract
Other assets	448,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(347,000)
Income (Loss) from Equity Method Investments	0
Archstone Transaction [Member]
Business Acquisition, Percentage of Voting Interests Acquired					60.00%
Properties acquired			71
Property Units Acquired			20,160
Partially Owned Consolidated Properties Acquired			1
Partially Owned Consolidated Units Acquired			432
Partially Owned Unconsolidated Properties Acquired			1
Partially Owned Unconsolidated Units Acquired			336
Master Leased Properties Acquired			3
Master Leased Units Acquired			853
Uncompleted Development Properties Acquired			4
Uncompleted Development Units Acquired			964
Land parcels acquired			14
Net assets acquired			$ 8,968,389,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			514,700,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual			352,800,000
Payments to Acquire Businesses, Net of Cash Acquired			4,000,000,000
Secured Debt			$ 2,000,000,000
Stock Issued During Period, Shares, New Issues | shares			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 | $ / shares			$ 55.99	$ 54.75
Noncash or Part Noncash Acquisition, Debt Assumed			$ 3,100,000,000
Mark-to-Market Debt Premiums			127,900,000
Proceeds from Sale of Other Assets			$ 4,500,000,000
Number Of Operating Properties Under Long Term Ground Leases			9
Land			$ 2,239,000,000
Depreciable property Abstract
Buildings and improvements			5,765,538,000
Furniture, fixtures and equipment			61,470,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			304,830,000
Projects under development			36,583,000
Land held for development			244,097,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities			230,608,000
Other assets			195,260,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other			(108,997,000)
Finite-Lived Intangible Asset, Off-market Lease, Favorable, Gross					$ 1,260,000
Off-market Lease, Unfavorable					2,400,000
Business Combination, Acquisition Related Costs	83,100,000
Payments of Financing Costs	13,500,000		2,500,000
Merger Expenses	69,600,000		19,900,000
Income (Loss) from Equity Method Investments	2,700,000	4,300,000	54,000,000
Business Acquisition, Pro Forma Revenue			2,485,438,000
Business Acquisition, Proforma Income Loss From Continuing Operations			203,286,000
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax			2,074,072,000
Business Acquisition, Pro Forma Net Income (Loss)			2,277,358,000
Business Acquisition, Proforma Net Income Available to Common Shares			$ 2,183,756,000
Business Acquisition, Pro Forma Earnings Per Share, Basic | $ / shares			$ 6.07
Business Acquisition, Proforma Weighted Average Common Shares Basic | shares			359,688,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted | $ / shares			$ 6.05
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted | shares			375,861,000
Severance Costs			$ 54,100,000
Archstone Transaction [Member] | DelayedDrawTermLoan [Member]
Term Loan Principal Amount			750,000,000
Archstone Transaction [Member] | Positive Outcome of Litigation [Member]
Depreciable property Abstract
Income (Loss) from Equity Method Investments	18,600,000
Archstone Transaction [Member] | ERPOP [Member]
Depreciable property Abstract
Business Acquisition, Pro Forma Revenue			2,485,438,000
Business Acquisition, Proforma Income Loss From Continuing Operations			203,286,000
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax			2,074,072,000
Business Acquisition, Pro Forma Net Income (Loss)			2,277,358,000
Business Acquisition, Proforma Net Income Available to Units			$ 2,273,798,000
Business Acquisition, Pro Forma Earnings Per Share, Basic | $ / shares			$ 6.07
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic | shares			373,421,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted | $ / shares			$ 6.05
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted | shares			375,861,000
Archstone Transaction [Member] | Consolidated Properties [Member]
Uncompleted Development Properties Acquired			2
Archstone Transaction [Member] | Unconsolidated Properties [Member]
Uncompleted Development Properties Acquired			2
Assets [Member]
Depreciable property Abstract
Below Market Lease, Gross	178,251,000	178,251,000			178,251,000
Finite-Lived Intangible Asset, Off-market Lease, Favorable, Gross	1,260,000	1,260,000
Liability [Member]
Depreciable property Abstract
Below Market Lease, Gross	5,270,000	5,270,000			$ 8,040,000
Off-market Lease, Unfavorable	$ 2,400,000	$ 2,400,000