Real Estate Real Estate (Details) (USD $)	12 Months Ended			48 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Land	$ 6,192,512,000	$ 4,554,912,000		$ 6,192,512,000
Property, Plant and Equipment [Abstract]
Investment Building and Building Improvements	17,509,609,000	14,135,740,000		17,509,609,000
Fixtures and Equipment, Gross	1,214,220,000	1,343,765,000		1,214,220,000
Finite-Lived Intangible Assets, Gross	502,218,000	232,439,000		502,218,000
Development in Process	988,867,000	387,750,000		988,867,000
Land Available for Development	393,522,000	353,823,000		393,522,000
Real Estate Investment Property, at Cost	26,800,948,000	21,008,429,000		26,800,948,000
Real Estate Investment Property, Accumulated Depreciation	(4,807,709,000)	(4,912,221,000)		(4,807,709,000)
Investment in real estate, net	21,993,239,000	16,096,208,000		21,993,239,000
Ground Lease Intangibles Below Market	178,251,000			178,251,000
Retail Lease Intangibles Above Market	1,260,000			1,260,000
Lease Intangible Assets	179,511,000			179,511,000
Accumulated Amortization Intangible Assets	(4,364,000)			(4,364,000)
Lease Intangible Assets, Net	175,147,000			175,147,000
Ground Lease Intangibles Above Market	2,400,000			2,400,000
Retail Lease Intangibles Below Market	5,500,000			5,500,000
Lease Intangible Liabilities	7,900,000			7,900,000
Amortization Of Intangible Liabilities	(1,161,000)			(1,161,000)
Lease Intangible Liabilities, net	6,739,000			6,739,000
Ground Lease Amortization	3,600,000
Retail Lease Amortization	2,700,000
Weighted Average Ground Lease Amortization Period	49.8			49.8
Weighted Average Retail Lease Amortization Period	2.8			2.8
Properties acquired		1
Master Leased Properties Acquired	3			3
Acquisition of Archstone, net of cash acquired	4,000,875,000	0	0
Mortgage notes payable	5,174,166,000	3,898,369,000		5,174,166,000
Stock Issued During Period, Shares, New Issues	34,468,085	25,023,919	3,866,666
Stock Issued During Period, Value, New Issues		192,300,000	201,900,000
Average Price Per Common Share Issued		$ 60.59	$ 52.23
Noncash or Part Noncash Acquisition, Debt Assumed	34,100,000	137,600,000
Mark-to-Market Debt Premiums	127,900,000
Number Of Operating Properties Under Long Term Ground Leases	13			13
Business Combination, Acquisition Related Costs	300,000	7,000,000	7,700,000	94,700,000
Payments of Financing Costs	16,526,000	21,209,000	20,421,000
Merger Expenses	19,864,000	5,619,000	1,736,000	81,200,000
(Loss) from investments in unconsolidated entities due to merger expenses	(54,004,000)	0	0
Business Acquisition, Pro Forma Revenue	2,485,438,000	2,317,699,000
Business Acquisition, Proforma Income Loss From Continuing Operations	203,286,000	(54,940,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	2,074,072,000	720,361,000
Business Acquisition, Pro Forma Net Income (Loss)	2,277,358,000	665,421,000
Business Acquisition, Proforma Net Income Available to Common Shares	2,183,756,000	622,424,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 6.07	$ 1.74
Business Acquisition, Proforma Weighted Average Common Shares Basic	359,688,000	356,984,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 6.05	$ 1.74
Business Acquisition, Proforma Weighted Average Number Of Shares Diluted	375,861,000	356,984,000
Consolidated Properties [Member]
Property, Plant and Equipment [Abstract]
Uncompleted Development Properties Acquired	2			2
Archstone [Member]
Property, Plant and Equipment [Abstract]
Acquisition of Archstone, net of cash acquired	4,000,000,000
Mortgage notes payable	2,000,000,000			2,000,000,000
Noncash or Part Noncash Acquisition, Debt Assumed	3,100,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Land	2,239,000,000			2,239,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	304,830,000			304,830,000
Business Combination Purchase Price Allocation Projects Under Development	36,583,000			36,583,000
Business Combination Purchase Price Allocation Land Held for Development	244,097,000			244,097,000
Business Combination Purchase Price Allocation Investments in Unconsolidated Entities	196,615,000			196,615,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets	195,260,000			195,260,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(112,107,000)			(112,107,000)
Payments of Financing Costs	2,500,000	8,400,000	2,600,000	13,500,000
Severance Costs	54,100,000
2014 [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Amortization 5 Year	4,321,000			4,321,000
Retail Lease Intangibles Amortization 5 Year	(1,010,000)			(1,010,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles 5 Year	3,311,000			3,311,000
2015 [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Amortization 5 Year	4,321,000			4,321,000
Retail Lease Intangibles Amortization 5 Year	(1,016,000)			(1,016,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles 5 Year	3,305,000			3,305,000
2016 [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Amortization 5 Year	4,321,000			4,321,000
Retail Lease Intangibles Amortization 5 Year	(908,000)			(908,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles 5 Year	3,413,000			3,413,000
2017 [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Amortization 5 Year	4,321,000			4,321,000
Retail Lease Intangibles Amortization 5 Year	(540,000)			(540,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles 5 Year	3,781,000			3,781,000
2018 [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Amortization 5 Year	4,321,000			4,321,000
Retail Lease Intangibles Amortization 5 Year	(71,000)			(71,000)
Total Above And Below Market Ground Lease Intangibles And Retail Lease Intangibles 5 Year	4,250,000			4,250,000
Building and Building Improvements [Member]
Property, Plant and Equipment [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	5,805,467,000			5,805,467,000
Furniture and Fixtures [Member]
Property, Plant and Equipment [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	61,470,000			61,470,000
Archstone Transaction [Member]
Property, Plant and Equipment [Abstract]
Ground Lease Intangibles Below Market	178,251,000			178,251,000
Retail Lease Intangibles Above Market	1,260,000			1,260,000
Ground Lease Intangibles Above Market	2,400,000			2,400,000
Retail Lease Intangibles Below Market	8,040,000			8,040,000
Business Acquisition, Percentage of Voting Interests Acquired	60.00%			60.00%
Properties acquired	71
Partially Owned Consolidated Properties Acquired	1			1
Partially Owned Consolidated Units Acquired	432			432
Partially Owned Unconsolidated Properties Acquired	1			1
Partially Owned Unconsolidated Units Acquired	336			336
Master Leased Properties Acquired	3			3
Master Leased Units Acquired	853			853
Uncompleted Development Properties Acquired	4			4
Uncompleted Development Units Acquired	964			964
Land parcels acquired	14
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	8,971,215,000			8,971,215,000
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
Number Of Operating Properties Under Long Term Ground Leases	9			9
Unconsolidated Properties [Member]
Property, Plant and Equipment [Abstract]
Uncompleted Development Properties Acquired	2			2
Projects under development [Member]
Property, Plant and Equipment [Abstract]
Land Under Development	353,574,000	210,632,000		353,574,000
Development in Process	635,293,000	177,118,000		635,293,000
Land held for development [Member]
Property, Plant and Equipment [Abstract]
Development in Process	52,133,000	58,955,000		52,133,000
Land Available for Development	341,389,000	294,868,000		341,389,000
Archstone Transaction [Member]
Property, Plant and Equipment [Abstract]
Property Units Acquired	20,160
OPERATING PARTNERSHIP
Land	6,192,512,000	4,554,912,000		6,192,512,000
Property, Plant and Equipment [Abstract]
Development in Process	988,867,000	387,750,000		988,867,000
Land Available for Development	393,522,000	353,823,000		393,522,000
Real Estate Investment Property, at Cost	26,800,948,000	21,008,429,000		26,800,948,000
Real Estate Investment Property, Accumulated Depreciation	(4,807,709,000)	(4,912,221,000)		(4,807,709,000)
Investment in real estate, net	21,993,239,000	16,096,208,000		21,993,239,000
Acquisition of Archstone, net of cash acquired	4,000,875,000	0	0
Mortgage notes payable	5,174,166,000	3,898,369,000		5,174,166,000
Payments of Financing Costs	16,526,000	21,209,000	20,421,000
Merger Expenses	19,864,000	5,619,000	1,736,000
(Loss) from investments in unconsolidated entities due to merger expenses	(54,004,000)	0	0
Business Acquisition, Pro Forma Revenue	2,485,438,000	2,317,699,000
Business Acquisition, Proforma Income Loss From Continuing Operations	203,286,000	(54,940,000)
Business Acquisition, Proforma Income Loss From Discontinued Operations Net Of Tax	2,074,072,000	720,361,000
Business Acquisition, Pro Forma Net Income (Loss)	2,277,358,000	665,421,000
Business Acquisition, Proforma Net Income Available to Units	2,273,798,000	651,548,000
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 6.07	$ 1.74
Business Acquisition, Proforma Weighted Average Limited Partnership And General Partnership Units Outstanding Basic	373,421,000	370,837,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 6.05	$ 1.74
Business Acquisition, Proforma Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding Diluted	375,861,000	370,837,000
Archstone Transaction [Member]
Property, Plant and Equipment [Abstract]
Stock Issued During Period, Shares, New Issues	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 [Abstract]
Term Loan Principal Amount	$ 750,000,000			$ 750,000,000
Consolidated Rental Properties [Member]
Property, Plant and Equipment [Abstract]
Properties acquired	1	9
Property Units Acquired	322	1,896
Land [Member]
Property, Plant and Equipment [Abstract]
Property Units Acquired	0	0
Land parcels acquired	1	6