Real Estate (Details) (USD $)	3 Months Ended										3 Months Ended				3 Months Ended			3 Months Ended					3 Months Ended				12 Months Ended	3 Months Ended		3 Months Ended	12 Months Ended	1 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2013 Consolidated Properties [Member]	Mar. 31, 2014 2014 [Member]	Mar. 31, 2014 2015 [Member]	Mar. 31, 2014 2016 [Member]	Mar. 31, 2014 2017 [Member]	Mar. 31, 2014 2018 [Member]	Mar. 31, 2014 2019 [Member]	Mar. 31, 2014 Archstone [Member]	Mar. 31, 2013 Archstone [Member]	Mar. 31, 2014 Building and Building Improvements [Member]	Mar. 31, 2014 Furniture and Fixtures [Member]	Mar. 31, 2013 Archstone Transaction [Member]	Mar. 31, 2014 Archstone Transaction [Member]	Mar. 31, 2013 Unconsolidated Properties [Member]	Mar. 31, 2013 Investment Banking and Legal/Accounting Fees [Member]	Mar. 31, 2014 Projects under development [Member]	Dec. 31, 2013 Projects under development [Member]	Mar. 31, 2014 Land held for development [Member]	Dec. 31, 2013 Land held for development [Member]	Mar. 31, 2013 Archstone Transaction [Member]	Mar. 31, 2014 OPERATING PARTNERSHIP	Mar. 31, 2013 OPERATING PARTNERSHIP	Dec. 31, 2013 OPERATING PARTNERSHIP	Dec. 31, 2012 Public Offering [Member]	Mar. 31, 2013 Archstone Transaction [Member]	Mar. 31, 2013 Term Loan [Member]	Mar. 31, 2014 Consolidated Rental Properties [Member]	Dec. 31, 2013 Consolidated Rental Properties [Member]	May 08, 2014 Land [Member]
Land	$ 6,281,124,000		$ 6,192,512,000																					$ 6,281,124,000		$ 6,192,512,000
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements	17,843,201,000		17,509,609,000
Fixtures and Equipment, Gross	1,273,171,000		1,214,220,000
Finite-Lived Intangible Assets, Gross	507,100,000		502,218,000
Land Under Development																			390,850,000	353,574,000
Projects under development	865,177,000		988,867,000																474,327,000	635,293,000	42,007,000	52,133,000		865,177,000		988,867,000
Land held for development	295,357,000		393,522,000																		253,350,000	341,389,000		295,357,000		393,522,000
Real Estate Investment Property, at Cost	27,065,130,000		26,800,948,000																					27,065,130,000		26,800,948,000
Real Estate Investment Property, Accumulated Depreciation	(4,992,877,000)		(4,807,709,000)																					(4,992,877,000)		(4,807,709,000)
Investment in real estate, net	22,072,253,000		21,993,239,000																					22,072,253,000		21,993,239,000
Ground Lease Intangibles Below Market	178,251,000		178,251,000													178,251,000
Retail Lease Intangibles Above Market	1,260,000		1,260,000													1,260,000
Lease Intangible Assets	179,511,000		179,511,000
Amortization of Intangible Assets	(5,502,000)		(4,364,000)
Lease Intangible Assets, Net	174,009,000		175,147,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000													2,400,000
Retail Lease Intangibles Below Market	5,500,000		5,500,000													8,040,000
Lease Intangible Liabilities	7,900,000		7,900,000
Amortization Of Intangible Liabilities	(1,471,000)		(1,161,000)
Lease Intangible Liabilities, net	6,429,000		6,739,000
Ground Lease Amortization	1,100,000	400,000
Retail Lease Amortization	300,000	100,000
Weighted Average Ground Lease Amortization Period	49.8
Weighted Average Retail Lease Amortization Period	2.8
Ground Lease Intangibles Amortization					3,241,000	4,321,000	4,321,000	4,321,000	4,321,000	4,321,000
Retail Lease Intangibles Amortization					(758,000)	(1,016,000)	(908,000)	(540,000)	(71,000)	(71,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles					2,483,000	3,305,000	3,413,000	3,781,000	4,250,000	4,250,000
Business Acquisition, Percentage of Voting Interests Acquired															60.00%
Properties acquired	1														71															1
Property Units Acquired	430																						20,160							430
Partially Owned Properties Acquired Properties															1
Partially Owned Units Acquired Units															432
Partially Owned Unconsolidated Properties Acquired															1
Partially Owned Unconsolidated Units Acquired															336
Master Leased Properties Acquired		3													3
Master Leased Units Acquired															853
Uncompleted Development Properties Acquired				2											4		2
Uncompleted Development Units Acquired															964
Land parcels acquired															14																	1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net																8,968,389,000
Payments to Acquire Businesses, Net of Cash Acquired	0	4,000,643,000										4,000,000,000												0	4,000,643,000
Mortgage notes payable	5,167,626,000		5,174,166,000									2,000,000,000												5,167,626,000		5,174,166,000
Issuance of Common Shares																											21,850,000	34,468,085
Stock Issued During Period, Value, New Issues																											1,200,000,000	1,900,000,000
Average Price Per Common Share Issued	$ 56.87																										$ 54.75	$ 55.99
Noncash or Part Noncash Acquisition, Debt Assumed											3,100,000,000
Mark-to-Market Debt Premiums		127,900,000
Proceeds From Sale Of Property																															4,500,000,000
Term Loan Principal Amount																													750,000,000
Number of Properties Subject to Ground Leases		9
Business Acquisition, Purchase Price Allocation, Land											2,239,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment													5,765,538,000	61,470,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets											304,830,000
Business Combination Purchase Price Allocation Projects Under Development											36,583,000
Business Combination Purchase Price Allocation Land Held for Development											244,097,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities											230,608,000
Business Acquisition, Purchase Price Allocation, Other Assets											195,260,000
Business Acquisition, Purchase Price Allocation, Other Liabilities											(108,997,000)
Business Combination, Acquisition Related Costs	94,700,000
Payments of Financing Costs	60,000	13,869,000									(13,500,000)	2,500,000												60,000	13,869,000
Merger Expenses	81,200,000	19,100,000																19,100,000
Income Loss From Equity Method Investments Merger Expenses		46,000,000
Business Acquisition, Pro Forma Revenue		638,499,000																							638,499,000
Business Acquisition, Proforma Income Loss From Continuing Operations		(34,473,000)																							(34,473,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax		1,213,615,000																							1,213,615,000
Business Acquisition, Pro Forma Net Income (Loss)		1,179,142,000																							1,179,142,000
Business Acquisition, Proforma Net Income Available to Common Shares		1,130,671,000
Business Acquisition, Proforma Net Income Available to Units																									1,178,887,000
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ 3.15																							$ 3.15
Business Acquisition, Pro Forma Earnings Per Share, Diluted		$ 3.15																							$ 3.15
Business Acquisition, Proforma Weighted Average Common Shares Basic		359,362,000
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted		359,362,000
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic																									373,085,000
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted																									373,085,000
Severance Costs												44,800,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual															52,600,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual															$ 36,200,000