Real Estate (Details) (USD $)	3 Months Ended		6 Months Ended		42 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012
Land	$ 6,264,787,000		$ 6,264,787,000		$ 6,264,787,000	$ 4,554,912,000
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements	17,862,440,000		17,862,440,000		17,862,440,000	14,135,740,000
Fixtures and Equipment, Gross	1,201,868,000		1,201,868,000		1,201,868,000	1,343,765,000
Finite-Lived Intangible Assets, Gross	504,665,000		504,665,000		504,665,000	232,439,000
Projects under development	585,749,000		585,749,000		585,749,000	387,750,000
Land held for development	569,398,000		569,398,000		569,398,000	353,823,000
Real Estate Investment Property, at Cost	26,988,907,000		26,988,907,000		26,988,907,000	21,008,429,000
Real Estate Investment Property, Accumulated Depreciation	(4,547,327,000)		(4,547,327,000)		(4,547,327,000)	(4,912,221,000)
Investment in real estate, net	22,441,580,000		22,441,580,000		22,441,580,000	16,096,208,000
Ground Lease Intangibles Below Market	178,251,000		178,251,000		178,251,000
Retail Lease Intangibles Above Market	2,310,000		2,310,000		2,310,000
Lease Intangible Assets	180,561,000		180,561,000		180,561,000
Lease Intangible Assets, Net	178,720,000		178,720,000		178,720,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000		2,400,000
Retail Lease Intangibles Below Market	7,790,000		7,790,000		7,790,000
Lease Intangible Liabilities	10,190,000		10,190,000		10,190,000
Amortization Of Intangible Liabilities	(610,000)		(610,000)		(610,000)
Lease Intangible Liabilities, net	9,580,000		9,580,000		9,580,000
Ground Lease Amortization	1,000,000		1,400,000
Retail Lease Amortization	100,000		200,000
Weighted Average Ground Lease Amortization Period	49.8		49.8		49.8
Weighted Average Retail Lease Amortization Period	5.3		5.3		5.3
Properties acquired			1
Property Units Acquired			322
Master Leased Properties Acquired	3		3		3
Payments to Acquire Businesses, Net of Cash Acquired			4,000,875,000	0
Mortgage notes payable	6,247,612,000		6,247,612,000		6,247,612,000	3,898,369,000
Issuance of Common Shares			34,468,085
Noncash or Part Noncash Acquisition, Debt Assumed			34,100,000
Mark-to-Market Debt Premiums			127,900,000
Number of Properties Subject to Ground Leases	9		9		9
Business Combination, Acquisition Related Costs			100,000	5,500,000	93,500,000
Payments of Financing Costs			(18,006,000)	(4,283,000)
Merger Expenses	467,000	685,000	19,559,000	1,834,000	80,000,000
(Loss) from investments in unconsolidated entities due to merger expenses	(6,999,000)	0	(53,010,000)	0
Business Acquisition, Pro Forma Revenue	635,078,000	589,929,000	1,256,088,000	1,158,374,000
Business Acquisition, Proforma Income Loss From Continuing Operations	96,585,000	(126,424,000)	60,541,000	(275,698,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	389,329,000	107,841,000	1,608,374,000	277,844,000
Business Acquisition, Pro Forma Net Income (Loss)	485,914,000	(18,583,000)	1,668,915,000	(2,146,000)
Business Acquisition, Proforma Net Income Available to Common Shares	467,237,000	(20,191,000)	1,601,368,000	(2,989,000)
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.30	$ (0.06)	$ 4.45	$ (0.01)
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.29	$ (0.06)	$ 4.44	$ (0.01)
Business Acquisition, Proforma Weighted Average Common Shares Basic	359,653,000	356,511,000	359,509,000	355,817,000
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted	375,910,000	356,511,000	375,722,000	355,817,000
Consolidated Properties [Member]
Property, Plant and Equipment, Gross [Abstract]
Uncompleted Development Properties Acquired	2		2		2
Archstone [Member]
Property, Plant and Equipment, Gross [Abstract]
Amortization of Intangible Assets	(1,841,000)		(1,841,000)		(1,841,000)
Payments to Acquire Businesses, Net of Cash Acquired			4,000,000,000
Mortgage notes payable	2,000,000,000		2,000,000,000		2,000,000,000
Noncash or Part Noncash Acquisition, Debt Assumed			3,100,000,000
Business Acquisition, Purchase Price Allocation, Land	2,239,000,000		2,239,000,000		2,239,000,000
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets	304,830,000		304,830,000		304,830,000
Business Combination Purchase Price Allocation Projects Under Development	36,583,000		36,583,000		36,583,000
Business Combination Purchase Price Allocation Land Held for Development	239,418,000		239,418,000		239,418,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities	185,723,000		185,723,000		185,723,000
Business Acquisition, Purchase Price Allocation, Other Assets	196,310,000		196,310,000		196,310,000
Business Acquisition, Purchase Price Allocation, Other Liabilities	(112,369,000)		(112,369,000)		(112,369,000)
Payments of Financing Costs			2,500,000		13,500,000
Merger Expenses				1,834,000
Severance Costs			50,900,000
2013 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	2,161,000		2,161,000		2,161,000
Retail Lease Intangibles Amortization	(300,000)		(300,000)		(300,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	1,861,000		1,861,000		1,861,000
2014 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,144,000)		(1,144,000)		(1,144,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,177,000		3,177,000		3,177,000
2015 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,150,000)		(1,150,000)		(1,150,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,171,000		3,171,000		3,171,000
2016 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(1,042,000)		(1,042,000)		(1,042,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,279,000		3,279,000		3,279,000
2017 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(674,000)		(674,000)		(674,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	3,647,000		3,647,000		3,647,000
2018 [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Amortization	4,321,000		4,321,000		4,321,000
Retail Lease Intangibles Amortization	(205,000)		(205,000)		(205,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles	4,116,000		4,116,000		4,116,000
Investment Banking and Legal/Accounting Fees [Member]
Property, Plant and Equipment, Gross [Abstract]
Merger Expenses			19,600,000
Building and Building Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	5,836,010,000		5,836,010,000		5,836,010,000
Furniture and Fixtures [Member]
Property, Plant and Equipment, Gross [Abstract]
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	61,470,000		61,470,000		61,470,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Ground Lease Intangibles Below Market	178,251,000		178,251,000		178,251,000
Retail Lease Intangibles Above Market	2,310,000		2,310,000		2,310,000
Ground Lease Intangibles Above Market	2,400,000		2,400,000		2,400,000
Retail Lease Intangibles Below Market	8,040,000		8,040,000		8,040,000
Business Acquisition, Percentage of Voting Interests Acquired	60.00%		60.00%		60.00%
Properties acquired			71
Partially Owned Properties Acquired Properties	1		1		1
Partially Owned Units Acquired Units	432		432		432
Partially Owned Unconsolidated Properties Acquired	1		1		1
Partially Owned Unconsolidated Units Acquired	336		336		336
Master Leased Properties Acquired	3		3		3
Master Leased Units Acquired	853		853		853
Uncompleted Development Properties Acquired	4		4		4
Uncompleted Development Units Acquired	964		964		964
Land parcels acquired			14
Business Acquisition, Purchase Price Allocation, Assets Acquired	8,986,975,000		8,986,975,000		8,986,975,000
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
Unconsolidated Properties [Member]
Property, Plant and Equipment, Gross [Abstract]
Uncompleted Development Properties Acquired	2		2		2
Projects under development [Member]
Property, Plant and Equipment, Gross [Abstract]
Land Under Development	224,561,000		224,561,000		224,561,000	210,632,000
Projects under development	361,188,000		361,188,000		361,188,000	177,118,000
Land held for development [Member]
Property, Plant and Equipment, Gross [Abstract]
Projects under development	63,018,000		63,018,000		63,018,000	58,955,000
Land held for development	506,380,000		506,380,000		506,380,000	294,868,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Property Units Acquired			20,160
OPERATING PARTNERSHIP
Land	6,264,787,000		6,264,787,000		6,264,787,000	4,554,912,000
Property, Plant and Equipment, Gross [Abstract]
Projects under development	585,749,000		585,749,000		585,749,000	387,750,000
Land held for development	569,398,000		569,398,000		569,398,000	353,823,000
Real Estate Investment Property, at Cost	26,988,907,000		26,988,907,000		26,988,907,000	21,008,429,000
Real Estate Investment Property, Accumulated Depreciation	(4,547,327,000)		(4,547,327,000)		(4,547,327,000)	(4,912,221,000)
Investment in real estate, net	22,441,580,000		22,441,580,000		22,441,580,000	16,096,208,000
Payments to Acquire Businesses, Net of Cash Acquired			4,000,875,000	0
Mortgage notes payable	6,247,612,000		6,247,612,000		6,247,612,000	3,898,369,000
Payments of Financing Costs			(18,006,000)	(4,283,000)
Merger Expenses	467,000	685,000	19,559,000	1,834,000
(Loss) from investments in unconsolidated entities due to merger expenses	(6,999,000)	0	(53,010,000)	0
Business Acquisition, Pro Forma Revenue	635,078,000	589,929,000	1,256,088,000	1,158,374,000
Business Acquisition, Proforma Income Loss From Continuing Operations	96,585,000	(126,424,000)	60,541,000	(275,698,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	389,329,000	107,841,000	1,608,374,000	277,844,000
Business Acquisition, Pro Forma Net Income (Loss)	485,914,000	(18,583,000)	1,668,915,000	(2,146,000)
Business Acquisition, Proforma Net Income Available to Units	485,693,000	(21,149,000)	1,668,439,000	(3,127,000)
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.30	$ (0.06)	$ 4.45	$ (0.01)
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.29	$ (0.06)	$ 4.44	$ (0.01)
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic	373,403,000	370,573,000	373,245,000	369,451,000
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted	375,910,000	370,573,000	375,722,000	369,451,000
Archstone Transaction [Member]
Property, Plant and Equipment, Gross [Abstract]
Issuance of Common Shares			34,468,085
Stock Issued During Period, Value, New Issues			1,900,000,000
Average Price Per Common Share Issued			$ 55.99
DelayedDrawTermLoan [Member]
Property, Plant and Equipment, Gross [Abstract]
Term Loan Principal Amount	$ 750,000,000		$ 750,000,000		$ 750,000,000
Land [Member]
Property, Plant and Equipment, Gross [Abstract]
Property Units Acquired			0
Land parcels acquired			1