Real Estate (Details) (USD $)	3 Months Ended		6 Months Ended		16 Months Ended		3 Months Ended		6 Months Ended									3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	16 Months Ended			3 Months Ended		6 Months Ended	16 Months Ended		6 Months Ended					3 Months Ended		6 Months Ended	12 Months Ended		6 Months Ended	12 Months Ended	6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Retail Site [Member]	Jun. 30, 2013 Retail Site [Member]	Jun. 30, 2014 Retail Site [Member]	Jun. 30, 2013 Retail Site [Member]	Jun. 30, 2014 Assets [Member]	Dec. 31, 2013 Assets [Member]	Mar. 31, 2013 Assets [Member]	Jun. 30, 2014 Liability [Member]	Dec. 31, 2013 Liability [Member]	Mar. 31, 2013 Liability [Member]	Mar. 31, 2013 Consolidated Properties [Member]	Jun. 30, 2014 Ground Lease [Member]	Jun. 30, 2013 Ground Lease [Member]	Jun. 30, 2014 Ground Lease [Member]	Jun. 30, 2013 Ground Lease [Member]	Mar. 31, 2013 Archstone [Member]	Jun. 30, 2013 Archstone [Member]	Jun. 30, 2014 Archstone [Member]	Mar. 31, 2013 Building and Building Improvements [Member]	Mar. 31, 2013 Furniture and Fixtures [Member]	Jun. 30, 2013 Archstone Transaction [Member]	Mar. 31, 2013 Archstone Transaction [Member]	Jun. 30, 2013 Archstone Transaction [Member]	Jun. 30, 2014 Archstone Transaction [Member]	Mar. 31, 2013 Unconsolidated Properties [Member]	Jun. 30, 2013 Investment Banking and Legal/Accounting Fees [Member]	Jun. 30, 2014 Projects under development [Member]	Dec. 31, 2013 Projects under development [Member]	Jun. 30, 2014 Land held for development [Member]	Dec. 31, 2013 Land held for development [Member]	Mar. 31, 2013 Archstone Transaction [Member]	Jun. 30, 2013 OPERATING PARTNERSHIP	Jun. 30, 2013 OPERATING PARTNERSHIP	Dec. 31, 2012 Public Offering [Member]	Mar. 31, 2013 Term Loan [Member]	Jun. 30, 2014 Consolidated Rental Properties [Member]	Dec. 31, 2013 Consolidated Rental Properties [Member]	Jun. 30, 2014 Land [Member]
Land			$ 6,296,735,000		$ 6,296,735,000	$ 6,192,512,000
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements			17,920,222,000		17,920,222,000	17,509,609,000
Fixtures and Equipment, Gross			1,302,882,000		1,302,882,000	1,214,220,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			507,633,000		507,633,000	502,218,000
Land Under Development																																	391,156,000	353,574,000
Projects under development			1,006,992,000		1,006,992,000	988,867,000																											615,836,000	635,293,000	50,089,000	52,133,000
Land held for development			306,625,000		306,625,000	393,522,000																													256,536,000	341,389,000
Real Estate Investment Property, at Cost			27,341,089,000		27,341,089,000	26,800,948,000
Real Estate Investment Property, Accumulated Depreciation			(5,170,438,000)		(5,170,438,000)	(4,807,709,000)
Investment in real estate, net			22,170,651,000		22,170,651,000	21,993,239,000
Below Market Lease, Gross											178,251,000	178,251,000	178,251,000	5,270,000	5,500,000	8,040,000
Finite-Lived Intangible Asset, Off-market Lease, Favorable, Gross		1,260,000	1,260,000		1,260,000	1,260,000
Finite-Lived Intangible Assets, Gross			179,511,000		179,511,000	179,511,000
Amortization of Intangible Assets			(6,641,000)		(6,641,000)	(4,364,000)
Lease Intangible Assets, Net			172,870,000		172,870,000	175,147,000
Off-market Lease, Unfavorable														2,400,000	2,400,000	2,400,000
Lease Intangible Liabilities			7,670,000		7,670,000	7,900,000
Amortization Of Intangible Liabilities			(1,678,000)		(1,678,000)	(1,161,000)
Lease Intangible Liabilities, net			5,992,000		5,992,000	6,739,000
Amortization of Intangible Assets			1,530,000	1,216,000			300,000	100,000	600,000	200,000								1,100,000	1,000,000	2,200,000	1,400,000
Weighted Average Ground Lease Amortization Period			49.8		49.8
Weighted Average Retail Lease Amortization Period			2.8		2.8
Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year			1,692,000		1,692,000		(469,000)		(469,000)									2,161,000		2,161,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months			3,382,000		3,382,000		(939,000)		(939,000)									4,321,000		4,321,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two			3,425,000		3,425,000		(896,000)		(896,000)									4,321,000		4,321,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three			3,781,000		3,781,000		(540,000)		(540,000)									4,321,000		4,321,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four			4,250,000		4,250,000		(71,000)		(71,000)									4,321,000		4,321,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five			4,250,000		4,250,000		(71,000)		(71,000)									4,321,000		4,321,000
Properties acquired			3																									71														3
Property Units Acquired			772																																		20,160					772
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
Master Leased Units Acquired																												853
Uncompleted Development Properties Acquired																	2											4			2
Uncompleted Development Units Acquired																												964
Land parcels acquired																												14
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net																												8,968,389,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual																											151,900,000		204,500,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual																											103,900,000		140,000,000
Payments to Acquire Businesses, Net of Cash Acquired			0	4,000,875,000																		4,000,000,000
Mortgage notes payable			5,158,091,000		5,158,091,000	5,174,166,000																2,000,000,000
Issuance of Common Shares																																								21,850,000
Stock Issued During Period, Value, New Issues																																								1,200,000,000
Average Price Per Common Share Issued																																								$ 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 Property			49,050,000																																							40,850,000	4,500,000,000	8,200,000
Term Loan Principal Amount																																									750,000,000
Number of Properties Subject to Ground Leases		9
Number of Real Estate Properties			397		397
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			100,000	100,000																										100,900,000
Payments of Financing Costs			10,881,000	18,006,000																			2,500,000	13,500,000
Payments for Merger Related Costs				19,600,000	87,400,000																											19,600,000
Income Loss From Equity Method Investments Merger Expenses			6,200,000	53,000,000
Business Acquisition, Pro Forma Revenue	635,078,000			1,256,088,000																																		635,078,000	1,256,088,000
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax	96,585,000			60,541,000																																		96,585,000	60,541,000
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	389,329,000			1,608,374,000																																		389,329,000	1,608,374,000
Business Acquisition, Pro Forma Net Income (Loss)	485,914,000			1,668,915,000																																		485,914,000	1,668,915,000
Business Acquisition, Proforma Net Income Available to Common Shares	467,237,000			1,601,368,000
Business Acquisition, Proforma Net Income Available to Units																																						485,693,000	1,668,439,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.30			$ 4.45																																		$ 1.30	$ 4.45
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.29			$ 4.44																																		$ 1.29	$ 4.44
Business Acquisition, Proforma Weighted Average Common Shares Basic	359,653,000			359,509,000
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted	375,910,000			375,722,000
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic																																						373,403,000	373,245,000
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted																																						375,910,000	375,722,000
Severance Costs																							$ 50,900,000